Methods and devices for ablation

ABSTRACT

An ablating device has a cover which holds an interface material such as a gel. The cover contains the interface material during initial placement of the device. The ablating device may also have a removable tip or a membrane filled with fluid. In still another aspect, the ablating device may be submerged in liquid during operation.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of application Ser. No.10/006,088, filed on Dec. 5, 2001, which is a continuation ofapplication Ser. No. 09/884,435, filed on Jun. 19, 2001, which is acontinuation-in-part of application Ser. No. 09/614,991, filed Jul. 12,2000, which is a continuation-in-part of application Ser. No. 09/507,336filed Feb. 18, 2000 which is a continuation-in-part of application Ser.No. 09/356,476, filed Jul. 19, 1999, which is a continuation-in-part ofapplication Ser. No. 09/157,824, filed Sep. 21, 1998, which is acontinuation-in-part of application Ser. No. 08/943,683, filed Oct. 15,1997, which is a continuation-in-part of application Ser. No.08/735,036, filed Oct. 22, 1996, the full disclosures of which areincorporated herein by reference.

FIELD OF THE INVENTION

This invention relates generally to devices and methods for ablatingtissue. The diagnosis and treatment of electrophysiological diseases ofthe heart, and more specifically to devices and methods for epicardialmapping and ablation for the treatment of atrial fibrillation, aredescribed in connection with the devices and methods of the presentinvention.

BACKGROUND OF THE INVENTION

Atrial fibrillation results from disorganized electrical activity in theheart muscle, or myocardium. The surgical maze procedure has beendeveloped for treating atrial fibrillation and involves the creation ofa series of surgical incisions through the atrial myocardium in apreselected pattern so as to create conductive corridors of viabletissue bounded by scar tissue.

As an alternative to the surgical incisions used in the maze procedure,transmural ablation of the heart wall has been proposed. Such ablationmay be performed either from within the chambers of the heart(endocardial ablation) using endovascular devices (e.g. catheters)introduced through arteries or veins, or from outside the heart(epicardial ablation) using devices introduced into the chest. Variousablation technologies have been proposed, including cryogenic,radiofrequency (RF), laser and microwave. The ablation devices are usedto create elongated transmural lesions—that is, lesions extendingthrough a sufficient thickness of the myocardium to block electricalconduction—which form the boundaries of the conductive corridors in theatrial myocardium. Perhaps most advantageous about the use of transmuralablation rather than surgical incisions is the ability to perform theprocedure on the beating heart without the use of cardiopulmonarybypass.

In performing the maze procedure and its variants, whether usingablation or surgical incisions, it is generally considered mostefficacious to include a transmural incision or lesion that isolates thepulmonary veins from the surrounding myocardium. The pulmonary veinsconnect the lungs to the left atrium of the heart, and join the leftatrial wall on the posterior side of the heart. This location createssignificant difficulties for endocardial ablation devices for severalreasons. First, while many of the other lesions created in the mazeprocedure can be created from within the right atrium, the pulmonaryvenous lesions must be created in the left atrium, requiring either aseparate arterial access point or a transeptal puncture from the rightatrium. Second, the elongated and flexible endovascular ablation devicesare difficult to manipulate into the complex geometries required forforming the pulmonary venous lesions and to maintain in such positionsagainst the wall of the beating heart. This is very time-consuming andcan result in lesions which do not completely encircle the pulmonaryveins or which contain gaps and discontinuities. Third, visualization ofendocardial anatomy and endovascular devices is often inadequate andknowing the precise position of such devices in the heart can bedifficult, resulting in misplaced lesions. Fourth, ablation within theblood inside the heart can create thrombus which, in the right chambers,is generally filtered out by the lungs rather than entering thebloodstream. However, on the left side of the heart where the pulmonaryvenous lesions are formed, thrombus can be carried by the bloodstreaminto the coronary arteries or the vessels of the head and neck,potentially resulting in myocardial infarction, stroke or otherneurologic sequelae. Finally, the heat generated by endocardial deviceswhich flows outward through the myocardium cannot be preciselycontrolled and can damage extracardiac tissues such as the pericardium,the phrenic nerve and other structures.

What are needed, therefore, are devices and methods for forming lesionsthat isolate the pulmonary veins from the surrounding myocardium whichovercome these problems. The devices and methods will preferably beutilized epicardially to avoid the need for access into the leftchambers of the heart and to minimize the risk of producing thrombus.

Additional aspects of the present invention are directed to devices andmethods for ablating tissue. Ablation of heart tissue and, specifically,ablation of tissue for treatment of atrial fibrillation is developed asa particular use of these other aspects of the present invention.

SUMMARY OF THE INVENTION

The present invention meets these and other objectives by providingepicardial ablation devices and methods useful for creating transmurallesions for the treatment of atrial fibrillation.

In a first embodiment, a method of forming a transmural lesion in a wallof the heart adjacent to the pulmonary veins comprises the steps ofplacing at least one ablation device through a thoracic incision andthrough a pericardial penetration so that at least one ablation deviceis disposed in contact with an epicardial surface of the heart wall;positioning at least one ablation device adjacent to the pulmonary veinson a posterior aspect of the heart while leaving the pericardialreflections intact; and ablating the heart wall with at least oneablating device to create at least one transmural lesion adjacent to thepulmonary veins. While the method may be performed with the heartstopped and circulation supported with cardiopulmonary bypass, themethod is preferably performed with the heart beating so as to minimizemorbidity, mortality, complexity and cost.

In another aspect of the invention, an apparatus for forming atransmural lesion in the heart wall adjacent to the pulmonary veinscomprises, in a preferred embodiment, an elongated flexible shaft havinga working end and a control end; an ablation device attached to theworking end for creating a transmural lesion in the heart wall; acontrol mechanism at the control end for manipulating the working end;and a locating device near the working end configured to engage one ormore of the pulmonary veins, or a nearby anatomical structure such as apericardial reflection, for positioning the working end adjacent to thepulmonary veins. The locating device may comprise a catch, branch, notchor other structure at the working end configured to engage one or moreof the pulmonary veins or other anatomical structure such as theinferior vena cava, superior vena cava, aorta, pulmonary artery, leftatrial appendage, right atrial appendage, or one of the pericardialreflections. The ablation device may be a radiofrequency electrode,microwave transmitter, cryogenic element, laser, ultrasonic transduceror any of the other known types of ablation devices suitable for formingtransmural lesions. Preferably, the apparatus includes a plurality ofsuch ablation devices arranged along the working end in a linear patternsuitable for forming a continuous, uninterrupted lesion around or on thepulmonary veins.

The working end may additionally include one or more movable elementsthat are manipulated from the control end and which may be moved into adesired position after the working end has been located near thepulmonary veins. Slidable, rotatable, articulated, pivotable, bendable,pre-shaped or steerable elements may be used. Additional ablationdevices may be mounted to these movable elements to facilitate formationof transmural lesions. The movable elements may be deployed to positionsaround the pulmonary veins to create a continuous transmural lesionwhich electrically isolates the pulmonary veins from the surroundingmyocardium.

In addition, a mechanism may be provided for urging all or part of theworking end against the epicardium to ensure adequate contact with theablation devices. This mechanism may be, for example, one or moresuction holes in the working end through which suction may be applied todraw the working end against the epicardium, or an inflatable balloonmounted to the outer side of the working end such that, upon inflation,the balloon engages the inner wall of the pericardium and forces theworking end against the epicardium. This also functions to protectextracardiac tissues such as the pericardium from injury by retractingsuch tissues away from the epicardial region which is being ablated,and, in the case of the balloon, providing an insulated barrier betweenthe electrodes of the ablation probe and the extracardiac tissues.

The apparatus may be either a single integrated device or two or moredevices which work in tandem. In either case, the apparatus may have twoor more tips at the working end which are positioned on opposing sidesof a tissue layer such as a pericardial reflection. A device may beprovided for approximating the two free ends on opposing sides of thetissue layer, such as an electromagnet mounted to one or both of thefree ends. In this way, a continuous lesion may be created in themyocardium from one side of the pericardial reflection to the otherwithout puncturing or cutting away the pericardial reflection.

The apparatus may further include a working channel through whichsupplemental devices may be placed to facilitate visualization, tissuemanipulation, supplementary ablation, suction, irrigation and the like.

The apparatus and methods of the invention are further useful formapping conduction pathways in the heart (local electrograms) for thediagnosis of electrophysiological diseases. Any of the electrodes on theapparatus may be individually selected and the voltage may be monitoredto determine the location of conduction pathways. Alternatively, theapparatus of the invention may be used for pacing the heart bydelivering current through one or more selected electrodes at levelssufficient to stimulate heart contractions.

Additionally, although the ablation apparatus and methods of theinvention are preferably configured for epicardial use, the principlesof the invention are equally applicable to endocardial ablationcatheters and devices. For example, an endocardial ablation apparatusaccording to the invention would include a locating device configured toengage an anatomical structure accessible from within the chambers ofthe heart such as the coronary sinus (from the right atrium), pulmonaryartery (from the right ventricle), or the pulmonary veins (from the leftatrium), and the ablation device would be positionable in apredetermined location relative to the locating device. The endocardialapparatus could further include suction holes, expandable balloons, orother mechanisms for maintaining contact between the ablation device andthe interior surface of the heart wall.

In another aspect of the present invention, an anchor is used to holdpart of the device while displacing another part of the device. Theanchor is preferably a balloon but may also be tines, a suction port ora mechanically actuated device. After actuating the anchor, a proximalportion of the device may be moved by simply manipulating the device orby advancement or withdrawal of a stylet.

The present invention is also related to a method of creating acontinuous ablation lesion in tissue underlying a pericardial reflectionwithout penetrating the pericardial reflection. First and secondablating devices are introduced into the space between the pericardiumand the epicardium. The first ablating device is positioned on one sideof the pericardial reflection and the second ablating device ispositioned on the other side of the pericardial reflection. Tissuebeneath the pericardial reflection is then ablated with one or both ofthe devices to create a continuous lesion beneath the pericardialreflection. The devices may be aligned across the pericardial reflectionby any suitable method such as with magnetic force, use of an emitterand sensor, or by marking the pericardial reflection on one side andlocating the mark from the other side of the pericardial reflection. Theemitter and sensor may work with electromagnetic radiation such aslight, ultrasound, magnetic field, and radiation.

In yet another aspect of the invention, the ablating device may have aguide portion which aligns the device between the pericardium andepicardium. The guide portion may be a continuous strap or a number ofdiscrete guide portions. The guide portions may be fins, wings or one ormore laterally extending elements such as balloons. The guide portionsmay be individually actuated to align the device and ablate discretelocations of the tissue along the ablating device.

The ablating device may also be advanced into position over a guide. Theguide is preferably a guidewire but may be any other suitable structure.The guide may also lock into position with a coaxial cable or lockingarm. The guide is advanced ahead of the ablation device and positionedalong the desired ablation path. The ablating device is then advanced orretracted along the guide. The ablating device preferably includes adevice for locating previously formed lesions so that subsequent lesionswill merge with a previously formed lesion to create a continuous,transmural lesion. The device for locating previously created lesionsmay be pacing and sensing electrodes or electrodes which simply measureelectrical impedance.

Although cutting through the pericardial reflections has certain risks,the methods and devices of the present invention may, of course, bepracticed while cutting through the pericardial reflections. Afterpenetrating through the pericardial reflection, the ablating device mayinterlock with another part of the same device or with a separatedevice.

In another method and device of the present invention, another ablatingdevice is provided which may be used to ablate any type of tissueincluding heart tissue for the reasons described herein. The ablatingdevice has a suction well and an ablating element. The suction welladheres the device to the tissue to be ablated. The device is preferablyused to ablate cardiac tissue from an epicardial location to form atransmural lesion. The device preferably includes a number of cellswhich each have a suction well and at least one ablating element. Thecells are coupled together with flexible sections which permit the cellsto displace and distort relative to one another. The device preferablyhas about 5-30 cells, more preferably about 10-25 cells and mostpreferably about 16 cells. The suction well has an inner lip and anouter lip. The inner lip forms a closed wall around the ablatingelement.

The device also has a fluid inlet and a fluid outlet for delivering andwithdrawing fluid from within the closed wall formed by the inner lip.The fluid is preferably a conductive fluid, such as hypertonic saline,which conducts energy from the ablating element, such as an RFelectrode, to the tissue. The fluid is preferably delivered along ashort axis of the ablating element so that the temperature change acrossthe ablating element is minimized.

The ablating elements are preferably controlled by a control system. Oneor more temperature sensors on the device are coupled to the controlsystem for use as now described. The control system may control ablationin a number of different ways. For example, the control system mayactivate one or more pairs of adjacent cells to form continuous lesionsbetween the adjacent cells. After ablation at the one or more adjacentcells, another pair of adjacent cells is activated to form anothercontinuous ablation segment. This process is continued until acontinuous lesion of the desired geometry is produced. In another modeof operation, the control system may activate every other or every thirdcell. Still another mode of operation is to activate only the ablatingelements which have low temperatures by using a multiplexer coupled tothe temperature sensors.

The control system may also conduct a thermal response analysis of thetissue to be ablated to determine the appropriate ablation technique.The tissue to be ablated is heated, or cooled, and the temperatureresponse of the tissue over time is recorded. The temperature responseis then analyzed to determine the appropriate ablation technique. Theanalysis may be a comparison of the temperature response against adatabase of temperature responses or may be a calculation which mayrequire user input as described below.

In a further aspect of the invention, the ablating element preferablyproduces focused ultrasound in at least one dimension. An advantage ofusing focused ultrasound is that the energy can be concentrated withinthe tissue. Another advantage of using focused ultrasound is that theenergy diverges after reaching the focus thereby reducing thepossibility of damaging tissue beyond the target tissue as compared tocollimated ultrasonic energy. When ablating epicardial tissue withcollimated ultrasound, the collimated ultrasound energy not absorbed bythe target tissue travels through blood and remains concentrated on arelatively small area when it reaches another surface such as theendocardial surface on the other side of a heart chamber. The presentinvention reduces the likelihood of damage to other structures since theultrasonic energy diverges beyond the focus and is spread over a largerarea. The focused ultrasound has a focal length of about 2 to 20 mm,more preferably about 2 to 12 mm and most preferably about 8 mm in atleast one dimension. The focused ultrasound also forms an angle of 10 to170 degrees, more preferably 30 to 90 degrees and most preferably about60 degrees as defined relative to a focal axis. The focused ultrasoundpreferably emits over 90%, and more preferably over 99%, of the energywithin the angles and focal lengths described above. The focusedultrasound may be produced in any manner and is preferably produced by acurved transducer with a curved layer attached thereto. The ultrasoundis preferably not focused, and may even diverge, when viewed along anaxis transverse to the focal axis.

The ultrasound transducers are preferably operated while varying one ormore characteristics of the ablating technique such as the frequency,power, ablating time, and/or location of the focal axis relative to thetissue. In a first treatment method, the transducer is activated at afrequency of 2-7 MHz, preferably about 3.5 MHz, and a power of 80-140watts, preferably about 110 watts, in short bursts. For example, thetransducer may be activated for 0.01-1.0 second and preferably about 0.4second. The transducer is inactive for 2-90 seconds, more preferably5-80 seconds, and most preferably about 45 seconds between activations.Treatment at this frequency in relatively short bursts produceslocalized heating at the focus. Energy is not absorbed as quickly intissue at this frequency as compared to higher frequencies so thatheating at the focus is less affected by absorption in the tissue.

In a second treatment method, the transducer is operated for longerperiods of time, preferably about 1-4 seconds and more preferably about2 seconds, to distribute more ultrasound energy between the focus andthe near surface. The frequency during this treatment is also 2-14 MHz,more preferably 3-7 MHz and preferably about 6 MHz. The transducer isoperated for 0.7-4 seconds at a power of 20-60 watts, preferably about40 watts. The transducer is inactive for at least 3 seconds, morepreferably at least 5 seconds and most preferably at least 10 secondsbetween each activation.

In a third treatment method, the ultrasonic transducer is activated at ahigher frequency to heat and ablate the near surface. The transducer ispreferably operated at a frequency of at least 6 MHz and more preferablyat least 10 MHz and most preferably about 16 MHz. The transducer isoperated at lower power than the first and second treatment methodssince ultrasound is rapidly absorbed by the tissue at these frequenciesso that the near surface is heated quickly. In a preferred method, thetransducer is operated at 2-10 watts and more preferably about 5 watts.The transducer is preferably operated until the near surface NStemperature reaches 70-85 degrees C.

In general, the treatment methods described above deliver energy closerand closer to the near surface NS with each subsequent treatment method.Such a treatment method may be practiced with other devices withoutdeparting from this aspect of the invention and, as mentioned below, maybe automatically controlled by the control system.

The device preferably has a number of cells with each cell having atleast one ablating element. After ablating tissue with all of the cells,gaps may exist between adjacent ablations. The tissue in the gaps ispreferably ablated by moving at least one of the ablating elements. Inone method, the entire device is shifted so that each cell is used asecond time to ablate one of the adjacent gaps. Yet another method ofablating tissue in the gaps is to tilt one or more of the ablatingelements to direct the ultrasound energy at the gaps between cells. Theablating element may be moved, tilted or pivoted in any suitable mannerand is preferably tilted with an inflatable membrane. The transducer mayalso simply be configured to direct ultrasound energy to tissue lyingbeneath the gaps between adjacent transducers. In this manner, thedevice does not need to be moved or tilted.

The device may be adhered to tissue with suction although suction is notrequired. The device may also have a membrane filled with a substancewhich transmits the ultrasound energy to the tissue. The membraneconforms to the tissue and eliminates air gaps between the device andtissue to be ablated. Alternatively, the device may have a solid elementwhich contacts the tissue and transmits the ultrasound energy to thetissue. The device may also be used with a gel applied to the tissuewhich transmits the ultrasound energy and eliminates air gaps.

The device may also have a number of ultrasound transducers with varyingcharacteristics. For example, the device may have cells which providefocused ultrasound having different focal lengths or which are intendedto operate at different frequencies or power. In this manner, the usermay select the appropriate cell to ablate a particular tissue structure.For example, it may be desirable to select an ablating element with asmall focal length and/or low power when ablating thin tissue.

An advantage of using ultrasound for ablating tissue is that thetransducer may be used for other measurements. For example, thetransducer may be used to provide temperature, tissue thickness,thickness of fat or muscle layers, and blood velocity data. Theultrasound transducer may also be used to assess the adequacy of contactbetween the device and the tissue to be ablated. These features findobvious use in the methods described herein and all uses of ultrasoundmentioned here, such as temperature feedback control, may beaccomplished using other methods and devices.

In another aspect of the invention, the ablating device has a coverwhich extends over the bottom surface of the ablating device. A fluidcavity is defined by a space between the cover and bottom surface. Aflowable material is positioned in the cavity. The device is positionedin the desired ablation position and the cover is then moved to exposethe bottom surface while leaving the flowable material positionedbetween the ablating device and the tissue to be ablated.

In still another aspect of the present invention, the device has aflexible tip which facilitates advancement of the device. The tippreferably extends for at least two inches and is free of any ablatingelements. The tip is also preferably removable so that the tip also doesnot interfere with creating a closed loop.

In yet another aspect of the present invention, a fluid environment iscreated around the heart and the ablating device is submerged in thefluid environment. The fluid environment helps to ensure that no airbubbles or gaps are present and also can help to regulate thetemperature by controlling the fluid temperature.

In still another aspect, a fluid-filled membrane is provided at thecontact or bottom surface of the device. The membrane preferablyconforms to the shape of the tissue to be ablated and may form a convexcontact surface. A fluid may also be circulated through the membrane toprovide cooling as necessary. The membrane may also have holes or may bepermeable to permit some of the fluid to leak from the membrane intocontact with the tissue being ablated.

Other aspects and advantages of the invention are disclosed in thefollowing detailed description and in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1A is side view of a left ablation probe according to theinvention.

FIG. 1B is a side view of a right ablation probe according to theinvention.

FIGS. 2A-2F are side views of a working end of the left ablation probeof FIG. 1A in various configurations thereof.

FIG. 3 is a side cross-section of the working end of the left ablationprobe of FIG. 1A.

FIG. 4 is a transverse cross-section of the shaft of the left ablationprobe of FIG. 1A.

FIGS. 5A-C are partial side cross-sections of the working end of theleft ablation probe of FIG. 1A, showing the deployment of a superiorsub-probe and inner probe thereof.

FIG. 6 is a side view of the left ablation probe of FIG. 1A.

FIG. 7 is a partial side cross-section of the handle of the leftablation probe of FIG. 1A.

FIG. 8 is an anterior view of the thorax of a patient illustrating thepositioning of the left and right ablation probes according to themethod of the invention.

FIG. 9 is a side view of the interior of a patient's thorax illustratingthe positioning of the left and right ablation probes according to themethod of the invention.

FIG. 10 is a posterior view of a patient's heart illustrating the use ofthe left and right ablation probes according to the method of theinvention.

FIG. 11 is a posterior view of a patient's heart illustrating atransmural lesion formed according to the method of the invention.

FIGS. 12 and 13 are side views of the left ablation probe of theinvention positioned on a patient's heart, showing a balloon and suctionports, respectively, on the inner probe.

FIG. 14A shows the ablating device having a pre-shaped distal portion.

FIG. 14B shows an alternative anchor.

FIG. 14C shows another anchor.

FIG. 14D shows still another anchor.

FIG. 15 shows the ablating device having a flexible distal portion whichis shaped with a stylet.

FIG. 16 is a cross-sectional view of the ablating device of FIGS. 14 and15 with three chambers of the balloon inflated.

FIG. 17 is a cross-sectional view of the ablating device of FIGS. 14 and15 with two chambers of the balloon inflated.

FIG. 18 shows the ablating device advanced into the transversepericardial sinus with the balloon deflated.

FIG. 19 shows the ablating device advanced into the transversepericardial sinus with the balloon inflated.

FIG. 20 shows the ablating device extending between the left and rightinferior pulmonary veins and another ablating device having an endsuperior to the right superior pulmonary vein.

FIG. 21 shows the ablating device moved toward the right superior andright inferior pulmonary veins.

FIG. 22 shows one of the ablating devices having an emitter and theother ablating device having a sensor for aligning the devices across apericardial reflection.

FIG. 23 shows the ablating device having a needle to deliver a markerwhich is located on the other side of the pericardial reflection.

FIG. 24 shows the ablating device having a number of discrete guideportions.

FIG. 25 shows the guide portions being inflatable balloons.

FIG. 26 shows selective inflation of the balloons for selective ablationalong the ablating device.

FIG. 27A shows the guide portions used when ablating around thepulmonary veins.

FIG. 27B shows the guide portions being inflatable when ablating aroundthe pulmonary veins.

FIG. 28 is a bottom view of another ablating device which is advancedover a guide.

FIG. 29 is a top view of the ablating device of FIG. 28.

FIG. 30 is a cross-sectional view of the ablating device of FIGS. 28 and29 along line A-A of FIG. 29.

FIG. 31 is another cross-sectional view of the ablating device of FIGS.28 and 29 along line B-B of FIG. 29.

FIG. 32 shows the guide advanced to a desired location with the balloondeflated.

FIG. 33 shows the ablating device advanced over the guide and creating afirst lesion.

FIG. 34 shows the ablating device creating a second lesion continuouswith the first lesion.

FIG. 35 shows the ablating device creating a third lesion continuouswith the second lesion.

FIG. 36 shows another ablating device having an expandable devicemovable thereon.

FIG. 37 is a cross-sectional view of the ablating device of FIG. 36.

FIG. 38 is an enlarged view of the cross-sectional view of FIG. 37.

FIG. 39 shows the ablating device with a piercing element in a retractedposition.

FIG. 40 shows the ablating device aligned across the pericardialreflection.

FIG. 41 shows the ablating device interlocked with another ablatingdevice on opposite sides of the pericardial reflection.

FIG. 42 shows a mechanism for locking the first and second ablatingdevices together.

FIG. 43 shows the piercing element engaging a lock on the other ablatingdevice.

FIG. 44 shows the ablating device passing through the pericardialreflection and interlocking with itself.

FIG. 45 shows the ablating devices interlocked across the pericardialreflections.

FIG. 46 shows the ablating device adhered to a pericardial reflectionwith suction.

FIG. 47 shows the penetrating element penetrating the pericardialreflection.

FIG. 48 shows the ablating device passing through the pericardialreflection.

FIG. 49 shows another ablating device.

FIG. 50 shows a buckle for forming a closed loop with the ablatingdevice.

FIG. 51 shows another buckle for forming the closed loop with theablating device.

FIG. 52 shows a bottom side of the ablating device of FIG. 49.

FIG. 53A is a cross-sectional view of the ablating device along line C-Cof FIG. 52.

FIG. 53B is an alternative cross-sectional view of the ablating devicealong line C-C of FIG. 52.

FIG. 54 is a cross-sectional view of the ablation device along line D-Dof FIG. 53A showing a fluid inlet manifold.

FIG. 55 is a cross-sectional view of an alternative embodiment of thedevice.

FIG. 56 shows a system for controlling the ablation device of FIG. 55.

FIG. 57 shows the device having two sets of lumens extending from eachend of the device toward the middle of the device.

FIG. 58 shows another ablating device.

FIG. 59 is an exploded view of a cell of the ablating device.

FIG. 60 is a cross-sectional view of the ablating device of FIG. 60.

FIG. 61 is a perspective view of a transducer with a layer attachedthereto.

FIG. 62 is an end view of the transducer and layer.

FIG. 63 is a plan view of the transducer and layer.

FIG. 64 shows another ablating device with a membrane filled with asubstance with transmits energy from the transducer to the tissue.

FIG. 65 shows the membrane inflated to move the focus relative to thetissue.

FIG. 66 shows another ablating device with a membrane which tilts thedevice when inflated.

FIG. 67 shows another ablating device.

FIG. 68 shows still another ablating device having at least two ablatingelements which have different ablating characteristics.

FIG. 69 is an isometric view of another ablating element which divergesin at least one dimension to ablate tissue beneath gaps between ablatingelements.

FIG. 70 is a side view of the ablating element of FIG. 69.

FIG. 71 shows still another device for ablating tissue.

FIG. 72 is a partial cross-sectional view showing three ablatingelements which are movable within a body of the device.

FIG. 73 shows the ablating elements with the body removed.

FIG. 74 shows the ablating device having a cover.

FIG. 75 shows a system for ablating tissue which provides a liquidenvironment around the heart.

FIG. 76 shows another system for providing a liquid environment aroundthe heart.

FIG. 77 shows another system for ablating tissue with a membraneextending over the ablating element.

FIG. 78 shows the membrane extending over a number of ablating elements.

FIG. 79 shows a flexible skirt surrounding the ablating element.

FIG. 80 shows another embodiment of the flexible skirt.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIGS. 1A-1B illustrate a first embodiment of the apparatus of theinvention. In this embodiment, the apparatus comprises a left ablationprobe 20, shown in FIG. 1A, and a right ablation probe 22, shown in FIG.1B, which work in tandem to form a transmural lesion isolating thepulmonary veins from the surrounding myocardium. Left ablation probe 20has a flexible shaft 21 extending to a working end 24 configured forinsertion into the chest cavity through a small incision, puncture oraccess port. Opposite working end 24, shaft 21 is attached to a controlend 26 used for manipulating the working end 24 from outside the chest.Shaft 21 is dimensioned to allow introduction through a small incisionin the chest, preferably in a subxiphoid location, and advanced to thepulmonary veins on the posterior side of the heart. Preferably, shaft 21is configured to be flexible about a first transverse axis to allowanterior-posterior bending and torsional flexibility, but relativelystiff about a second transverse axis perpendicular to the firsttransverse axis to provide lateral bending stiffness. In an exemplaryembodiment, shaft 21 has a length in the range of about 10-30 cm, and aguide portion 25 having a rectangular cross-section with awidth-to-height ratio of about 2-5, the cross-sectional width beingabout 6-35 mm and the cross-sectional height being about 3-17 mm. Theguide portion 25 aligns the device between the epicardium andpericardium to ablate tissues as described below. Shaft 21 is made of aflexible biocompatible polymer such as polyurethane or silicone, andpreferably includes radiopaque markers or a radiopaque filler such asbismuth or barium sulfate.

Working end 24 includes a plurality of ablating elements 27. Theablating elements 27 are preferably a plurality of electrodes 28 fordelivering radiofrequency (RF) current to the myocardium so as to createtransmural lesions of sufficient depth to block electrical conduction.Electrodes 28 may be partially-insulated solid metal rings or cylinders,foil strips, wire coils or other suitable construction for producingelongated lesions. Electrodes 28 are spaced apart a distance selected sothat the lesions created by adjacent electrodes contact or overlap oneanother, thereby creating a continuous, uninterrupted lesion in thetissue underlying the electrodes. In an exemplary embodiment, electrodes28 are about 2-20 mm in length and are spaced apart a range of 1-6 mm.It is understood that the term electrodes 28 as used herein may refer toany suitable ablating element 27. For example, as an alternative to RFelectrodes, the ablating elements 27 may be microwave transmitters,cryogenic element, laser, heated element, ultrasound, hot fluid or othertypes of ablation devices suitable for forming transmural lesions. Theheated element may be a self-regulating heater to prevent overheating.Electrodes 28 are positioned so as to facilitate lesion formation on thethree-dimensional topography of the left atrium. For example, lateralelectrodes 28 a face medially to permit ablation of the myocardium onthe lateral side of the left inferior pulmonary vein and medialelectrodes 28 b face anteriorly to permit ablation of the posteriorsurface of the myocardium adjacent to the left inferior pulmonary vein.

Working end 24 further includes a locating mechanism which locates theworking end at one of the pulmonary veins and helps to maintain it inposition once located. In a preferred embodiment, working end 24 isbifurcated into two branches 30, 32, and the locating mechanism is anotch 34 disposed between the two branches. Notch 34 tapers into aconcave surface 36 so as to receive one of the pulmonary veins betweenbranches 30, 32 and to atraumatically engage the pulmonary vein againstconcave surface 36. In an exemplary embodiment, notch 34 is about 10 to30 mm in width at its widest point between branches 30, 32 and taperstoward concave surface 36 which has a radius of curvature of about 4 to15 mm, so as to conform to the outer curvature of the pulmonary vein.Preferably, notch 34 is sized and positioned for placement against theleft inferior pulmonary vein, as described more fully below.Alternatively, the locating mechanism may be configured to engageanother anatomic structure such as the inferior vena cava, superior venacava, pericardial reflections, pulmonary vein, aorta, pulmonary artery,atrial appendage, or other structure in the space between thepericardium and the myocardium. The various shapes of the ablatingdevices described and shown herein are, of course, useful in locatingvarious structures to position the ablating elements againstpredetermined tissues to be ablated.

Working end 24 further includes a superior sub-probe 38 and an inferiorsub-probe 40 which are slidably extendable from working end 24, asfurther described below.

Control end 26 includes a handle 42 and a plurality of slidableactuators 44A-44E, which are used to extend superior sub-probe 38 andinferior sub-probe 40 from working end 24, and to perform otherfunctions as described below. An electrical connector 46 suitable forconnection to an RF generator is mounted to handle 42 and iselectrically coupled to electrodes 28 at working end 24. Also mounted tohandle 42 are a working port 48 in communication with a working channel92, described below, and a connector 50 for connection to a source ofinflation fluid or suction, used for purposes described below.

Right ablation probe 22 has a flexible shaft 52 extending from a controlend 54 to a working end 56. Working end 56 has a cross-member 58 towhich are mounted a plurality of electrodes 60. Cross member 58preferably has tips 59 which are pre-shaped or deflectable into a curveso as to conform to the right lateral walls of the right pulmonaryveins, and which are separated by a distance selected so that the tworight pulmonary veins may be positioned between them, usually a distanceof about 20-50 mm. Electrodes 60 are sized and positioned so as tocreate a continuous lesion along the right side (from the patient'sperspective) of the pulmonary veins as described more fully below. In anexemplary embodiment, electrodes 60 are about 2-20 mm in length, and arespaced apart about 1-6 mm. Shaft 52 is dimensioned to allow introductionthrough a small incision in the chest, preferably in a subxiphoidlocation, and advanced to the pulmonary veins on the posterior side ofthe heart. Shaft 52 will have dimensions, geometry and materials likethose of shaft 21 of left ablation probe 20, described above.

Control end 54 includes a handle 62. An electrical connector 64 adaptedfor connection to an RF generator is attached to handle 62 and iselectrically coupled to electrodes 60 at working end 56. An inflation orsuction connector 65 is mounted to handle 62 and adapted for connectionto a source of inflation fluid or suction, for purposes described below.Handle 62 may further include a working port (not shown) like workingport 48 described above in connection with left ablation probe 20.

FIGS. 2A-2E illustrate the deployment of the various components ofworking end 24 of left ablation probe 20. Superior sub-probe 38 isslidably extendable from working end 24 as shown in FIG. 2B. A pluralityof electrodes 66 are mounted to superior sub-probe 38 and are sized andpositioned to create a continuous lesion along the left side of thepulmonary veins. Superior sub-probe 38 has an articulated or steerablesection 68 which can be selectively shaped into the position shown inFIG. 2C, with its distal tip 70 pointing in a lateral direction relativeto the more straight proximal portion 72.

As shown in FIG. 2D, an inner probe 74 is slidably extendable fromsuperior sub-probe 38 and is directed by steerable section 68 in alateral direction opposite notch 34. Inner probe 74 is separated fromnotch 34 by a distance selected such that inner probe 74 may bepositioned along the superior side of the pulmonary veins when the leftinferior pulmonary vein is positioned in notch 34. In an exemplaryembodiment, the maximum distance from concave surface 36 to inner probe74 is about 20-50 mm. A plurality of electrodes 76 are mounted to innerprobe 74 and positioned to enable the creation of a continuoustransmural lesion along the superior side of the pulmonary veins asdescribed more fully below.

Referring to FIG. 2E, inferior sub-probe 40 is slidably extendable fromworking end 24. Its distal tip 78 is attached to a tether 80 extendingthrough a lumen in shaft 21. Tether 80 may be selectively tensioned todraw distal tip 78 away from inner probe 74 (toward control end 26),imparting a curvature to inferior sub-probe 40. Inferior sub-probe 40 isconstructed of a resilient, bendable plastic which is biased into astraight configuration. When inferior sub-probe 40 has been advancedsufficiently, tether 80 may be released, whereby the resiliency ofinferior sub-probe 40 causes it to conform to the pericardial reflectionand the medial and/or inferior sides of the four pulmonary veins.Inferior sub-probe 40 further includes a plurality of electrodes 82sized and positioned to produce a continuous transmural lesion in themyocardium along the inferior side of the pulmonary veins, as describedmore fully below.

Referring to FIGS. 3 and 4, superior sub-probe 38 is slidably disposedin a first lumen 84 and inferior sub-probe 40 is slidably disposed in asecond lumen 86 in shaft 21. Electrodes 28 along notch 34 are coupled towires 88 disposed in a wire channel 90 running beneath electrodes 28 andextending through shaft 21. Each electrode is coupled to a separate wireto allow any electrode or combination of electrodes to be selectivelyactivated. Shaft 21 also includes a working channel 92 extending to anopening 94 in working end 24 through which instruments such asendoscopes, suction/irrigation devices, mapping and ablation devices,tissue retraction devices, temperature probes and the like may beinserted. Superior sub-probe 38 has an inner lumen 96 in which innerprobe 74 is slidably disposed. Electrodes 76 on inner probe 74 arecoupled to wires 98 extending through inner probe 74 to connector 46 onhandle 42, shown in FIG. 1A. Similarly, electrodes 66 on superiorsub-probe 38 are coupled to wires 99 (FIG. 4) and electrodes 82 oninferior sub-probe 40 are coupled to wires 100, both sets of wiresextending to connector 46 on handle 42. Tether 80 slidably extendsthrough tether lumen 102 in shaft 21.

The distal end of inner probe 74 has a tip electrode 104 for extendingthe transmural lesion produced by electrodes 76. Preferably, inner probe74 further includes a device for approximating the tip of inner probe 74with the superior tip 106 of right ablation probe 22 (FIG. 1B) when thetwo are separated by a pericardial reflection. In a preferredembodiment, a first electromagnet 108 is mounted to the distal end ofinner probe 74 adjacent to tip electrode 104. First electromagnet 108 iscoupled to a wire 110 extending to handle 42, where it is coupled to apower source and a switch (not shown) via connector 46 or a separateconnector. Similarly, a second electromagnet 112 is mounted to distaltip 78 of inferior sub-probe 40, adjacent to a tip electrode 114, whichare coupled to wires 116, 118 extending to a connector on handle 42. Asshown in FIG. 1B, a third electromagnet 120 is mounted to superior tip106 of right ablation probe 22, and a fourth electromagnet 122 ismounted to inferior tip 124 of right ablation probe 22. Electromagnets120, 122 are coupled to wires (not shown) extending to a connector onhandle 62 for coupling to a power source and switch. In this way,superior tip 106 and inferior tip 124 may be approximated with innerprobe 74 and inferior sub-probe 40 across a pericardial reflection byactivating electromagnets 108, 112, 120, 122.

It should be noted that thermocouples, thermistors or other temperaturemonitoring devices may be mounted to the working ends of either left orright ablation probes 20, 22 to facilitate temperature measurement ofthe epicardium during ablation. The thermocouples may be mountedadjacent to any of the electrodes described above, or may be welded orbonded to the electrodes themselves. The thermocouples will be coupledto wires which extend through shafts 21, 52 alongside the electrodewires to connectors 46, 64 or to separate connectors on handles 42, 62,facilitating connection to a temperature monitoring device.

FIGS. 5A-5C illustrate the operation of superior sub-probe 38. Superiorsub-probe 38 has a pull wire 126 movably disposed in a wire channel 128in a sidewall adjacent to inner lumen 96. Pull wire 126 is fixed at itsdistal end 130 to steerable section 68 of superior sub-probe 38.Steerable section 68 is constructed of a flexible, resilient plasticsuch that by tensioning pull wire 126, steerable section 68 may bedeformed into a curved shape to direct inner probe 74 in a transversedirection relative to the straight proximal portion 72, as shown in FIG.5B. Once in this curved configuration, inner probe 74 may be slidablyadvanced from superior sub-probe 38 as shown in FIG. 5C.

Referring to FIG. 6, actuator 44D is slidably disposed in a longitudinalslot 132 in handle 42 and is coupled to the proximal end of inferiorsub-probe 40. Actuator 44E is slidably disposed in a longitudinal slot134 in handle 42 and is coupled to the proximal end of tether 80. Whensub-probe 40 is to be deployed, actuator 44D is slid forward, advancinginferior sub-probe 40 distally. Actuator 44E may be allowed to slideforward as well, or it may be held in position to maintain tension ontether 80, thereby bending sub-probe 40 into the curved shape shown inFIG. 2E. When sub-probe 40 has been fully advanced, actuator 44E may bereleased, allowing distal end 78 of sub-probe 40 to engage thepericardial reflection along the inferior surfaces of the pulmonaryveins, as further described below.

Actuators 44A-C are slidably disposed in a longitudinal slot 136 inhandle 42, as more clearly shown in FIG. 7. Actuator 44A is attached tothe proximal end of superior sub-probe 38, and may be advanced forwardto deploy the sub-probe from working end 24, as shown in FIG. 2A.Actuator 44B is attached to inner probe 74, which is frictionallyretained in inner lumen 96 such that it is drawn forward with superiorsub-probe 38. Actuator 44C is attached to pull wire 126 which is alsodrawn forward with superior sub-probe 38. In order to deflect thesteerable section 68 of superior sub-probe 38, actuator 44C is drawnproximally, tensioning pull wire 126 and bending steerable section 68into the configuration of FIG. 2C. Finally, to deploy inner probe 74,actuator 44B is pushed forward relative to actuators 44A and 44C,advancing inner probe 74 from superior sub-probe 38 as shown in FIG. 2D.

The slidable relationship between the shafts and probes 74, 40, 38 helpsto guide and direct the probes to the tissues to be ablated. The shaftshave various features, including the ablating elements 27, however, theshafts may be simple sheaths which locate structures and/or direct theprobes into various regions of the pericardial space.

Referring now to FIGS. 8-11, a preferred embodiment of the method of theinvention will be described. Initially, left ablation probe 20 and rightablation probe 22 are connected to an RF generator 140. RF generator 140will preferably provide up to 150 watts of power at about 500 kHz, andwill have capability for both temperature monitoring and impedancemonitoring. A suitable generator would be, for example, a Model No.EPT-1000 available from the EP Technologies Division of BostonScientific Corp. of Natick, Mass. Retraction, visualization, temperaturemonitoring, suction, irrigation, mapping or ablation devices may beinserted through working port 142. Left ablation probe 20 may further beconnected to a source of suction or inflation fluid 144, for reasonsdescribed below. If electromagnets are provided on left and rightablation probes 20, 22 as described above, an additional connection maybe made to a power supply and switch for operating the electromagnets,or power may be supplied by RF generator 140 through connectors 46, 64.

A subxiphoid incision (inferior to the xiphoid process of the sternum)is made about 2-5 cm in length. Under direct vision through suchincision or by visualization with an endoscope, a second small incisionis made in the pericardium P (FIG. 9). Left ablation probe 20 isintroduced through these two incisions and advanced around the inferiorwall of the heart H to its posterior side under fluoroscopic guidanceusing fluoroscope 146. Alternative methods of visualization includeechocardiography, endoscopy, transillumination, and magnetic resonanceimaging. Left ablation probe 20 is positioned such that left inferiorpulmonary vein LI is disposed in notch 34 as shown in the posterior viewof the heart in FIG. 10.

Superior sub-probe 38 is then advanced distally from working end 24until its steerable section 68 is beyond the superior side of the leftsuperior pulmonary vein LS. Steerable section 68 is then deflected intothe curved configuration shown in FIG. 10 such that its distal end 70 issuperior to the left superior pulmonary vein LS and pointing rightwardtoward the right superior pulmonary vein RS. Inner probe 74 is thenadvanced toward the right until its distal tip is very close to orcontacting the pericardial reflection PR superior to the right superiorpulmonary vein RS.

Inferior sub-probe 40 is next advanced from working end 24 whilemaintaining tension on tether 80 such that the inferior sub-probeengages and conforms to the shape of the pericardial reflection PRbetween the left inferior and right inferior pulmonary veins. Wheninferior sub-probe 40 has been fully advanced, tension is released ontether 80 so that distal tip 78 moves superiorly into engagement withthe right inferior pulmonary vein RI adjacent to pericardial reflectionPR inferior thereto.

Right ablation probe 22 is placed through the subxiphoid incision andpericardial incision and advanced around the right side of the heart asshown in FIG. 8. Under fluoroscopic guidance, right ablation probe 22 ispositioned such that cross-member 58 engages the right superior andinferior pulmonary veins, as shown in FIG. 10. In this position,superior tip 106 and inferior tip 124 should be generally in oppositionto distal tip 75 of inner probe 74 and distal tip 78 of inferiorsub-probe 40, respectively, separated by pericardial reflections PR. Inorder to ensure close approximation of the two tip pairs, electromagnets108, 120, 114, 122 may be energized, thereby attracting the tips to eachother across the pericardial reflections RS.

It should be noted that the pericardium P attaches to the heart at thepericardial reflections PR shown in FIGS. 10-11. Because of theposterior location of the pulmonary veins and the limited access andvisualization available, cutting or puncturing the pericardialreflections in the vicinity of the pulmonary veins poses a risk ofserious injury to the heart or pulmonary veins themselves. The apparatusand method of the present invention avoid this risk by allowing thepericardial reflections to remain, intact, without any cutting orpuncturing thereof, although the pericardial reflections may also be cutwithout departing from the scope of the invention.

RF generator 140 is then activated to deliver RF energy to electrodes28, 60, 66, 76, 82, 104, and 112 on left and right ablation probes 20,22, producing the transmural lesion L shown in FIG. 11. Preferably,power in the range of 20-150 watts is delivered at a frequency of about500 kHz for a duration of about 30-180 seconds, resulting in localizedmyocardial temperatures in the range of 45-95° C. Ultrasoundvisualization may be used to detect the length, location and/or depth ofthe lesion created. Lesion L forms a continuous electrically-insulatedboundary encircling the pulmonary veins thereby electrically isolatingthe pulmonary veins from the myocardium outside of lesion L.

Ablation probes 20, 22 may further be used for mapping conductionpathways in the heart (local electrocardiograms) for the diagnosis ofelectrophysiological abnormalities. This is accomplished by selectingany of the electrodes on the ablation probes and monitoring the voltage.A commercially available electrophysiology monitoring system isutilized, which can select any electrode on the ablation probes andmonitor the voltage. Various electrodes and various locations on theheart wall may be selected to develop a map of potential conductionpathways in the heart wall. If ablation treatment is then required, thesteps outlined above may be performed to create transmural lesions atthe desired epicardial locations.

During any of the preceding steps, devices may be placed through workingport 142 and working channel 92 to assist and supplement the procedure.For example, a flexible endoscope may be introduced for visualization toassist positioning. Ultrasound probes may be introduced to enhancevisualization and for measuring the location and/or depth of transmurallesions. Suction or irrigation devices may be introduced to clear thefield and remove fluid and debris. Tissue manipulation and retractiondevices may be introduced to move and hold tissue out of the way.Cardiac mapping and ablation devices may also be introduced to identifyconduction pathways and to supplement the ablation performed by left andright ablation probes 20, 22.

Furthermore, mapping and ablation catheters, temperature monitoringcatheters, and other endovascular devices may be used in conjunctionwith the left and right ablation probes of the invention by introducingsuch devices into the right atrium or left atrium either through thearterial system or through the venous system via the right atrium and atranseptal puncture. For example, an ablation catheter may be introducedinto the left atrium to ablate any region of the myocardium notsufficiently ablated by left and right ablation probes 20, 22 in orderto ensure complete isolation of the pulmonary veins. Additionally,ablation catheters may be introduced into the right chambers of theheart, or epicardial ablation devices may be introduced throughincisions in the chest, to create other transmural lesions.

In some cases, it may be desirable to actively ensure adequate contactbetween the epicardium and the electrodes of left and right ablationprobes 20, 22. For this purpose, left ablation probe 20 and/or rightablation probe 22 may include one or more expandable devices such asballoons which are inflated in the space between the heart and thepericardium to urge the ablation probe against the epicardial surface.An exemplary embodiment is shown in FIG. 12, in which a balloon 150 ismounted to the outer surface of inner probe 74 opposite electrodes 76 onleft ablation probe 20. Inner probe 74 further includes an inflationlumen 152 in communication with an opening 154 within balloon 150 andextending proximally to inflation fitting 50 on handle 42, through whichan inflation fluid such as liquid saline or gaseous carbon-dioxide maybe delivered. When inflated, balloon 150 engages the inner surface ofthe pericardium P and urges inner probe 74 against the epicardialsurface of heart H. This ensures close contact between electrodes 76 andthe epicardium, and protects extracardiac tissue such as the pericardiumand phrenic nerve from injury caused by the ablation probes. Balloons orother expandable devices may similarly be mounted to superior sub-probe38, inferior sub-probe 40, or right ablation probe 22 to ensuresufficient contact between the epicardium and the electrodes on thosecomponents.

Alternatively or additionally, suction ports may be provided in theablation probes of the invention to draw the electrodes against theepicardium, as shown in FIG. 13. In an exemplary embodiment, suctionports 156 are disposed in inner probe 74 between or adjacent toelectrodes 76. Suction ports 156 are in communication with a suctionlumen 158 which extends proximally to suction fitting 48 on handle 42.In this way, when suction is applied through suction port 156, innerprobe 74 is drawn tightly against the heart, ensuring good contactbetween electrodes 76 and the epicardium. In a similar manner, superiorsub-probe 38, inferior sub-probe 40 and right ablation probe 22 mayinclude suction ports adjacent to the electrodes on those components toenhance contact with the epicardium.

Referring to FIGS. 14A, 15, 16 and 17, the ablating device 20 is shownwith various features described above. The embodiments are specificallyreferred to as ablating device 20A and like or similar reference numbersrefer to like or similar structure. The ablating device 20A may have anyof the features of the ablating devices 20, 22 described above and alldiscussion of the ablating devices 20, 22 or any other ablating devicedescribed herein is incorporated here. As mentioned above, the ablatingdevice 20A may have a pre-shaped portion 160 or a flexible or bendableportion 162 as shown in FIGS. 14 and 15, respectively. A stylet 164 orsheath (not shown) is used to shape the ablating device 20A as describedbelow. The stylet 164 passes through a working channel 166 which mayreceive other devices as described above. The working channel 166 mayalso be coupled to a source of fluid 169, such as fluoroscopic contrast,which may be used for visualization. The contrast may be any suitablecontrast including barium, iodine or even air. The fluoroscopic contrastmay be introduced into the pericardial space to visualize structures inthe pericardial space.

Referring to FIG. 14A, the pre-shaped portion 160 has a curved orL-shape in an unbiased position. The distal portion of the device 20Amay have any other shape such as a hook or C-shape to pass the device20A around a structure. The stylet 164 holds the pre-shaped portion 160in any other suitable geometry, such as dotted-line 167, forintroduction and advancement of the ablating device 20A. The stylet 164may also be malleable. When the ablating device 20A is at theappropriate position, the stylet 164 is withdrawn thereby allowing thedistal end 160 to regain the angled or curved shape. The device 20A mayalso be shaped with a sheath (not shown) through which the device 20Apasses in a manner similar to the manner of FIGS. 2 and 5.

Referring to FIG. 15, the ablating device 20A has the flexible distalportion 162 which is shaped by the stylet 164 into the dotted line 168position. The pre-shaped portion 160 may be used to position or advancethe ablating device 20A between the epicardium and pericardium. FIG. 18shows the pre-shaped portion positioned around the left superiorpulmonary vein as described below. A number of different stylets 164 maybe used to shape the flexible portion 162 around various structures.

The ablating device 20A also has an anchor 170 to anchor a portion ofthe device 20A while moving another part of the device 20A. When theanchor 170 is the balloon 150, the balloon may have a number of chambers171, preferably three, which can be inflated as necessary to positionthe device as shown in FIGS. 16 and 17. The chambers 171 are coupled toa source of inflation fluid 173 via inflation lumens 175. The anchor 170is preferably an expandable element 172 such as the balloon 150, but mayalso be tines which grab the epicardium, pericardium or pericardialreflection. The anchor 170 may also be one or more suction ports 156, asdescribed above (see FIG. 13). The suction ports 156 may be used toanchor the device to the pericardium, epicardium, pericardial reflectionor any other structure in the space between the pericardium andepicardium. Although only one anchor 170 is located at the distal end,the anchor 170 may be positioned at any other location and more than oneanchor 170 may be provided without departing from the scope of theinvention.

Referring to FIGS. 18-21, a specific use of the ablating device 20A isnow described. The ablating devices described herein may, of course, beused to ablate other tissues when positioned in the space between theepicardium and pericardium. The ablating device 20A is preferablyintroduced in the same manner as the ablating device 20 or in any othersuitable manner. When the ablating device 20A is at the entrance to thetransverse pericardial sinus, the ablating device 20A may be given theangled or curved shape by advancing or withdrawing the stylet 164 (seeFIGS. 14 and 15) or with the sheath (see FIGS. 2 and 5). The device 20Ais then advanced until the tip meets the pericardial reflection at theend of the sinus as shown in FIG. 18. The anchor 170, such as theballoon 150, is then actuated to resist movement of the distal end whendisplacing other parts of the ablating device 20A (FIG. 19). At thistime, the ablating device 20A may be used to ablate tissue in the mannerdescribed above from a position superior to the right superior pulmonaryvein, around the left superior pulmonary vein and to the left inferiorpulmonary vein. Thus, the ablating device 20A is similar to the ablatingdevice 20 described above in that the device 20A extends through thetransverse pericardial sinus and to the left inferior pulmonary vein.

The ablating device 20A, like the ablating device 20, may also have aportion 176 which is moved to ablate tissue inferior to the left andright inferior pulmonary veins. Stated another way, the portion 176 ismoved to a position inferior to the inferior pulmonary veins. Theportion 176 is moved into the position shown in FIG. 20 by simplypushing the device 20A to displace the portion 176 or by advancing orwithdrawing the stylet 164. After the ablating device 20A is properlypositioned, the ablating elements 27 are activated as described above tocreate transmural lesions.

Still referring to FIG. 20, another ablating device 22A may also be usedto ablate tissue in the same manner as the ablating device 22 describedabove. The ablating device 22A is introduced in the manner describedabove and is advanced until distal end 177 is positioned at a desiredlocation. FIG. 20 shows the distal end 177 superior to the rightsuperior pulmonary vein adjacent to the pericardial reflection. Aportion 179 of the ablating device 20A is then moved to the position ofFIG. 21 in any manner described above such as by introduction orwithdrawal of the stylet 164. The ablating device 20A is then used toablate tissue as described above.

The ablating device 20A, 22A are also similar to the ablating devices20, 22 in that the ablating devices 20A, 22A create continuous lesionson both sides of the pericardial reflections extending between the venacava and the right superior and right inferior pulmonary veins. Tissuebeneath the pericardial reflections is ablated using at least one of theablating devices 20A, 22A. The ablating devices 20A, 22A may beapproximated using any suitable technique or device such as withmagnetic force described above. Other methods and devices for creating acontinuous lesion beneath a pericardial reflection are described below.

Referring now to FIG. 22, another system and method for approximatingthe ablating devices 20, 22 and 20A, 22A is now described. An energyemitter 180, such as a light source 182, emits energy from the ablatingdevice 20A which is received by a sensor 184 on the other ablatingdevice 22A to determine when the devices 20A, 22A are positioned onopposite sides of a pericardial reflection. The emitter 180 and sensor184 preferably pass through the working channel 166 but may also beintegrated into the devices 20A, 22A. When the ablating devices 20A, 22Aare aligned across the pericardial reflection, the sensor 184 detectsproper alignment so that the lesion may be formed continuously on bothsides of the pericardial reflection.

Yet another method to make sure that the ablating devices 20A, 22A arealigned across a pericardial reflection is to mark a location on thepericardial reflection where a lesion has been created as shown in FIG.23. The device 20A has a needle 185 introduced through the workingchannel 166. The needle 185 delivers a marker 186, such as a radioopaquedye, which can be visualized. The device 20A may also deliver a solidmarker such as a platinum wire. An advantage of using the marker 186 isthat both ablating devices 20A, 22A do not need to be positioned onopposite sides of the pericardial reflection at the same time. Thus,only one ablating device 20A may be necessary to create a continuouslesion beneath the pericardial reflection since the same device 20A canmark the pericardial reflection on one side, locate the mark 186 on theother side, and continue the lesion on the other side of the pericardialreflection.

Referring again to FIG. 10, the ablating device 20 has the guide portion25. As mentioned above, the guide portion 25 preferably has a width toheight ratio of about 2 to 5. The guide portion 25 aligns the ablatingelement 27 against a predetermined structure, such as the pulmonaryveins, to ablate tissue. The relatively flat configuration of the guideportion 25 aligns the device 20 between the epicardium and thepericardium so that the ablating elements 27 are directed toward themyocardium.

Referring now to FIG. 24, an ablating device 20B is shown which has anumber of discrete guide portions 25A. Four guide portions 25A are shownin FIG. 24 with each guide portion 25A being shaped similar to a fin 29.The ablating device 20A may also have a beaded or scalloped appearance.The ablating device 20A preferably has flexible sections 188 between theguide portions 25A which provide torsional flexibility so that the guideportions 25A can rotate relative to one another. The guide portions 25Amay be positioned between the pulmonary veins as shown in FIG. 27A. Theablating device 20B may have any of the features of the other ablatingdevices 20, 20A described herein.

Referring to FIG. 25, another ablating device 20C is shown which hasguide portions 25B which may also be deployed after the ablating device20C has been positioned so that the guide portion 25B does not interferewith advancement and placement. The guide portion 25B has one or moreexpanding elements 192, such as the balloons 150, which may be expandedduring advancement or after the device 20A is at the desired location.The expanding elements 192 are positioned on opposite sides of theablating device 20C, however, the expanding elements 192 may bepositioned only on one side of the device 20C. The guide portions 25Amay be positioned between the pulmonary veins as shown in FIG. 27B. Theexpanding elements 192 may also be mechanically actuated elements suchas bending arms or an expandable mesh.

The expanding elements 192 may also be inflated at selected locationscorresponding to discrete ablation sites as shown in FIG. 26. Anadvantage of individual expansion of the expanding elements 192 is thatother portions of the device 20C may rotate and displace as necessary toprovide good contact at the desired ablation site 193.

Another ablating device 20D is now described with reference to FIGS.28-31. The ablating device 20D is advanced over a guide 260 which isadvanced ahead of the device 199. The guide 200 is preferably aguidewire 202 having the anchor 170 to anchor an end 204 of the guide200. The guide 200 is advanced and positioned along the intendedablation path. The ablating device 20D is then retracted or advancedalong the guide 200 to create a continuous lesion along the intendedablation path. The guide 200 may also be locked into a desiredorientation with a coaxial cable or with a mechanism similar to lockingarms used to hold surgical devices. The ablating device 20D has anexpanding device 201, such as the balloon 150, to move the ablatingelement 27 into contact with the tissue to be ablated. The balloon 150preferably has a number of chambers 203, preferably at least two,coupled to inflation lumens 205, 207 which are coupled to the source ofinflation fluid 173 (FIG. 14A). Electrodes 191, 193 are coupled to wires209, 211 passing through the device 20D. The guide 200 passes throughthe working channel 166. Wires 213 are also provided to steer, rotateand position the device 20D.

The ablating device 20D and/or the guide 200 preferably includes adevice 206 for aligning the ablating element with a previously createdlesion. The aligning device 206 may be electrodes 191, 193 which simplymeasure electrical impedance. When the electrodes 191, 193 measure alarge increase in electrical impedance an ablation is positioned beneaththe electrodes 191, 193. In this manner, the ablating element 27 can bealigned and positioned to create a continuous lesion through the tissue.Referring to FIG. 29, the electrodes 191, 193 may also be used to locatethe previously created lesion 195 as shown in FIG. 29. The electrode 191will sense a higher amplitude of activity than the electrode 193 sincethe electrode is positioned over the previously created lesion while theelectrode 191 is not.

Still referring to FIG. 28, the ablating device 20D may have first andsecond electrodes 194, 196 on opposite sides of the ablating element 27.The first electrode 194 may be a pacing electrode 195 which emits anelectrical impulse and the second electrode 196 may be a sensingelectrode 197 which receives electrical impulses. When the firstelectrode 194 emits a stimulus, launching a cardiac impulse, the impulseis transmitted through tissue to the sensing electrode 197 if adiscontinuity exists in the lesion. A number of sensing electrodes 197may be positioned along the ablating device 20A which may be used todetermine the location of a discontinuity. Both electrodes 194, 196 mayalso be sensing electrodes 197 with both electrodes 194, 196 merelysensing normal activity. When only one of the electrodes 194, 196 sensesthe activity an effective, continuous, transmural lesion has beencreated. The electrodes described herein may be coupled to any suitabledevice including an ECG with electrogram amplitudes being measured.

The electrodes 194, 196 may also be used to locate the end of apreviously created lesion. The time between emission of the pacingstimulus to receipt of the cardiac impulse at the sensing electrodeincreases when a transmural ablation has been created between theelectrodes 194, 196. When such an increase is detected, it is known thatthe previously created lesion is positioned between the electrodes 194,196. The time between emission and receipt of the cardiac impulse mayalso be used in simple time of flight analysis to determine the locationof a discontinuity in the ablation. For example, the electrodes 194, 196are positioned at a discontinuity in an ablation when the time of flightis lowest.

A method of using the device is shown in FIGS. 32-35. The guide 200 isadvanced to a desired location and the anchor 170 is actuated. Theablating device 20D is then advanced over the guide 200, the balloon 150is inflated, and a first ablation 215 is performed. The balloon 150 isthen deflated and the ablating device 20C is then moved to anotherlocation. The electrodes 191, 193 or 194, 196, or other suitablealigning device, is used to position and align the ablating device 20Dand a second ablation 217 is then performed which is continuous with thefirst ablation 215. The device 20D is then moved again and a thirdablation 219 is formed continuous with the second ablation 217.

Referring to FIGS. 36-38, another ablating device 210 is shown whereinthe same or similar reference numbers refer to the same or similarstructure. The ablating device 210 has an expandable structure 209,preferably a balloon 150A, movable along the ablating device 210 toselectively anchor and align the device 210. An advantage of the systemof FIGS. 36-38 is that the structure 209 can be moved to variouslocations on the ablating device 210 for moving various ablatingelements into contact with tissue to be ablated. The ablating device 210also has the anchor 170, such as the balloon 150B, to anchor a part ofthe ablating device 210 and to move the ablating elements 27 intocontact with the tissue to be ablated. The balloon 150B is coupled to asource of inflation fluid 211 via inflation lumen 223.

The expandable device 209 is mounted to a body 211 having a scallopedappearance to provide flexibility although any other suitable design maybe used. The body 211 has a C-shaped cross-section which engages aflange 221 on the ablating device 210. The expandable device 209 ispreferably the balloon 150A but may be a mechanically actuated device.For example, the expandable device 209 can be an extendable arm, a wireloop or an expandable mesh. The anchor 170 may be selectively expandableto guide, rotate, and move the ablating device 210 as necessary. Theballoon 150A preferably has at least two separately inflatable chambers212 and FIG. 38 shows the balloon 150A having three independentlyinflatable chambers 212. The chambers 212 are coupled to inflationlumens 219 which are coupled to a source of inflation fluid 213. Thechambers 212 may be inflated as necessary to move and rotate theablating device 210 and press the ablating element 27 against the tissueto be ablated. The expandable structure 209 is moved to variouspositions along the ablating device 210 to move various ablatingelements 27 into contact with the tissue. The body 211 may also havepull wires 218 for further manipulation of the ablating device 210.

As mentioned above, penetrating the pericardial reflections carriesinherent risks. However, the methods and devices of the invention may,of course, be used when penetrating the pericardial reflections. Theablating devices 20, 22, 20A, 22A may have a penetrating element 220 asshown in FIGS. 39-43 for penetrating the pericardial reflections. Thepenetrating element 220 is movable from a retracted position (FIG. 40)to an extended position (FIG. 41). The penetrating element 220 passesthrough the working channel 166 of the ablating device 20A. Thepenetrating element 220 is preferably positioned in the working channel166 but may also be integrated into the ablating device 20A or may be aseparate device altogether. The first and second ablating devices 20A,22A are positioned on opposite sides of the pericardial reflection asshown in FIG. 40 using the emitter and sensor arrangement describedabove in connection with FIG. 22 although any other devices ortechniques may be used. The penetrating element 220 is then used topenetrate the pericardial reflection and the two devices 20A, 22A areinterlocked as shown in FIG. 41.

Referring to FIGS. 42 and 43, the ablating device 22A has a lockingmechanism 224 which holds the penetrating element 220. The lockingmechanism 224 has a stationary jaw 230 and a movable jaw 231. Themovable jaw 231 is movable in the direction of arrow 223 for releasingthe device 20A. The locking mechanism 224 is also positioned in theworking channel 166 of the ablating device 22A but may be integral withthe device 22A. The penetrating element 220 preferably has a conical tip222 or other cutting element for piercing the pericardial reflection butmay also be a laser, ultrasonic dissector, or electrosurgical device.The penetrating element 220 may also be a blade, needle or otherstructure for cutting or piercing the pericardial reflection. Afterablating tissue, the locking mechanism 224 is released, the penetratingelement 220 is retracted and the ablating devices 20A, 22A are removed.The ablating devices 20A, 22A may have any other interlockingconfiguration and the ablating device 22A may interlock with some otherstructure other than the penetrating element 220. Referring to FIG. 48,the ablating devices 20, 22 may interlock with one another in the mannerdescribed above. Referring to FIG. 44, the ablating device 20 maypenetrate through one or more pericardial reflections and interlock withanother part of the ablating device 20. Referring to FIG. 45, theablating device 20 and the ablating device 22 may also interlock acrossthe pericardial reflections using the penetrating element 220 or othersuitable device.

Referring to FIGS. 46-49, another method of penetrating and advancingthrough the pericardial reflection is shown. The end of the ablatingdevice 20A may be adhered to the pericardial reflection using suctionthrough the working channel 166. The penetrating element 220 is thenadvanced through the working channel 166 while suction is maintained sothat the piercing element is guided directly to the pericardialreflection. The penetrating element 220 is then used to penetrate thepericardial reflection as shown in FIG. 45. The ablating device 20A isthen advanced through the pericardial reflection as shown in FIG. 46.

Referring to FIG. 14B, another anchor 170A for anchoring the device isshown. Any of the anchors described herein may be used with any of thedevices described herein without departing from the scope of theinvention. The anchor 170A is a relatively flat balloon having athickness of about 1 cm and a width of about 0.3 cm when the balloon isinflated. Referring to FIG. 14C, yet another inflatable anchor 170B isshown which forms a hook-shaped element 171 which can engage a vesselsuch as the aorta, superior or inferior vena cava or any other vesselmentioned herein. Referring to FIG. 14D, still another anchor 170C isshown which has a mechanically expanding coiled section 173. Asmentioned above, the anchors of the present invention are expanded tohold the devices at a particular location. For example, the anchors maybe used to anchor a part of the device between blood vessels such as thesuperior vena cava and the aorta. When positioned between blood vesselsor when engaging a vessel with the hook-shaped element of FIG. 14C,tension may be applied to the device to wrap the device around a vesselor vessels, such as the pulmonary veins, in the manner described above.

Referring to FIG. 49-54, another device 300 for ablating tissue, such ascardiac tissue, is shown. The device 300 may also be used in any mannerdescribed herein and may have the features and dimensions of otherdevices described herein without departing from the scope of theinvention. The device 300 encircles the pulmonary veins and isparticularly suited for conventional open chest surgery but may also beused in less and minimally invasive procedures. Although ablation oftissue around the pulmonary veins is described as a specific use of thedevice 300, the device 300 may be used on other parts of the heart andin other areas of the body.

The device 300 has a body 302 having a length of 5-12 inches, preferablyabout 10 inches, and a width of 0.2-0.7 inch preferably about 0.5 inch.The body 302 is preferably made of an polymeric material such assilicone or urethane and is formed by injection molding although anysuitable material and method may be used to form the body 302. The body302 has a number of cells 304 coupled together by integrally formedhinges 303 in the body 302. Of course, the cells 304 may be coupledtogether with mechanical connections rather than the integrally formedhinges 303 without departing from the scope of the invention. The device300 preferably has 5-30 cells, more preferably 10-25 cells and mostpreferably about 16 cells although any number of cells 304 may be useddepending upon the specific application. For example, the device 300 maybe used to extend around a single vessel, such as the aorta, pulmonaryvein, SVC or IVC in which case the device 300 preferably has 4-12 cells304 and preferably about 8 cells 304.

The device 300 has a locking mechanism 306, preferably a buckle 308,which engages another part of the device 300 to form a closed loop 307.Referring to FIG. 49, the device 300 extends around the pulmonary veinswith the locking mechanism 306 to form the closed loop 307 around thepulmonary veins. The buckle 308 forms a side-by-side (FIG. 50) or one ontop of the other (FIG. 51) locking engagement with another part of thedevice 300. Although the buckle 308 is preferred, the locking mechanism306 may have any other suitable structure for locking one part of thedevice 300 to another part of the device 300.

Referring now to FIGS. 49, 52, 53A and 54, the cells 304 have a suctionwell 310 for adhering the device to the tissue to be ablated. Thesuction well 310 may take any form and is preferably formed between aninner lip 312 and an outer lip 314. The suction well 310 has a suctionport 316 coupled to a vacuum source 318 through a lumen 320. The vacuumsource 318 is activated to cause the suction well 310 to hold the cell304 against the tissue to be ablated. The lumen 320 is preferably formedby a separate tube 322 bonded to the body 302. The lumen 320 may, ofcourse, be formed integral with the rest of the body 302. The uppersurface of the cells 304 has three longitudinal recesses 324 in whichthe tubes 322, 326, 328 are positioned. The tubes 322, 326, 328 haveslack between the cells 304 to permit the cells 304 to wrap aroundstructures without significant resistance from the tubes 322, 326, 328.

The suction port 316 preferably has a cross-sectional size which is nomore than 10% of the cross-sectional size of the lumen 320. In thismanner, if suction is lost at one of the cells 304, suction can bemaintained at the other cells 304 since the relatively small suctionport 316 produces low flow. Of course, another part of the vacuum flowpath 317 other than the suction port 316 may be sized small to reducelosses through cells 304 not adhered to the tissue.

An ablating element 311 is positioned within a closed wall 319 formed bythe inner lip 312 so that the ablating element 311 is surrounded by thesuction well 310. The ablating element 311 may be any ablating elementmentioned herein and a preferred element is an RF electrode 330. The RFelectrode 330 is coupled to an RF generator 332 which transmits RFenergy to the electrode. The RF electrode 330 is preferably a stainlesssteel or gold plated copper electrode although any suitable electrodemay be used. The ablating element 311 preferably has a width of 1-6 mm,preferably about 3 mm, and a length of 2-25 mm, preferably about 12 mm.When the ablating element 311 is the RF electrode, the ablating element311 is preferably spaced apart from the target tissue, or from a bottomof the inner lip 312, by a distance of 0.5-3 mm and more preferablyabout 1.5 mm. The locking mechanism 306 preferably has at least oneablating element 311 to create a continuous lesion in tissue beneath thelocking mechanism 306.

The ablating elements 311 are coupled to a control system 334 with wires345. The control system 334 controls ablation in the manner describedbelow. The RF generator 332 may form part of the control system 334 ormay be separate from the control system 334. One or more temperaturesensors 336, preferably thermocouples 338, are positioned withinrecesses in the inner and/or outer lips 312, 314 to measure temperature.The temperature sensors 336 are coupled to the control system 334 foruse as described below. Wires 340 extending through the tube 326 couplethe temperature sensors 336 to the control system 334.

Fluid is delivered to cool the tissue and/or conduct energy from theablating element 311 to the tissue. Fluid is supplied from a source offluid 342 to an inlet lumen 344 formed by tube 328. Fluid is withdrawnthrough the lumen 320 in the tube 322 so that the lumen 320 producessuction at the suction well 310 and withdraws fluid. As mentioned above,the lumens 344, 346 are preferably formed by the tubes 322, 328 but maybe integrally formed with the rest of the body 302. The fluid ispreferably a conductive solution, such as saline or hypertonic saline,which conducts RF energy from the electrode 330 to the tissue to beablated.

Referring to FIGS. 53A and 54, fluid flows from the inlet lumen 344 intoan inlet manifold 350 which distributes fluid along the length of theablating element 311 as shown in the cross-sectional view of FIG. 54.Fluid then flows into a fluid chamber 348 formed between the ablatingelement 311, inner lip 312 and tissue. Fluid passes across the fluidchamber 348 and is received at a fluid outlet manifold 352. The fluidoutlet manifold 352 is coupled to the lumen 320 so that the lumen 320withdraws fluid and provides suction for the suction well 310 asmentioned above.

The fluid inlet and outlet 350, 352 are preferably positioned onopposite sides of the short axis of the fluid chamber 348, however, thefluid inlet and fluid outlet 350, 352 may be positioned anywhere withinthe fluid chamber 348 without departing from the scope of the invention.Fluid is preferably supplied at an average flow rate of at least 0.24cc/sec, more preferably at least 0.50 cc/sec and most preferably atleast 1.0 cc/sec to each cell 304 although lower or higher flows may beused. Fluid is preferably delivered to the inlet lumen 344 at a setpressure which results in the desired average flow rate through thecells 304. The fluid may be cooled, or even heated, by passing the fluidthrough a heat exchanger 354. The fluid is preferably delivered at atemperature of no more than 40° C. and more preferably no more than 20°C. to cool the tissue and/or ablating element 311. A fluid permeable,porous structure, such as gauze (not shown), may be positioned in thefluid chamber 348 to hold the fluid and prevent direct contact betweenthe ablating element 311 and tissue.

Referring to FIG. 53B, the device 300E may also provide cooling to abackside 353 of the ablating element 311. Fluid from the inlet lumen 344passes across the backside 353 of the ablating element 311 and isremoved on the other side through the lumen 320. The embodiment of FIG.53B may include any of the features and advantages of the embodiment ofFIG. 35, for example, the fluid flow rate and temperature may be thesame as described in relation to FIG. 53A. The inlet lumen 344 is alsocoupled to the suction well 310 via a conduit 355 for supplying fluid tothe suction well 310. In this manner, the fluid may also be used to cooltissue adjacent to the ablating element 311. Fluid introduced into thesuction well 310 is withdrawn through the lumen 320 in the mannerdescribed above. Although the fluid in the suction well 310 is exposedto the near surface NS of the tissue, the cooling fluid may also becontained within a closed circuit so that the near surface NS of thetissue is not in direct contact with the fluid. Furthermore, the fluidpreferably cools tissue around the entire ablating element 311 but mayalso cool tissue only along one side of the device or only on the twolateral sides of the device without departing from the scope of theinvention.

Referring to FIGS. 55 and 56, another device 300E is shown where thesame or similar reference numbers refer to the same or similarstructure. Use and dimensions of the device 300 are equally applicablefor the device 300E. The device 300E has a lumen 356 contained within acavity 358 in the body 302E. The lumen 356 carries the wires 340, 345for the temperature sensors 336 and ablating elements 311. The lumen 356is coupled to the control system 334 for control in the manner describedbelow. The lumen 346 is a dedicated lumen for withdrawing fluid so thatthe fluid can be recycled as shown in FIG. 56. The system of FIG. 56 isdescribed in greater detail below in connection with use of the devices300, 300E. The lumen 356, wires 340, 345, ablating elements 311, andtemperature sensors 336 form a strip 359 which is bonded to the rest ofthe body 302, preferably with an interlocking engagement.

A pair of wires 360, 362 is positioned across a gap 361 in suction path363 (shown in dotted-line) to determine when the inner lip 312 is notadequately adhered to the tissue. When the inner lip 312 is notadequately adhered to the tissue, fluid leaks under the inner lip 312and is drawn into the vacuum outlet 316. The fluid, which is preferablycooled hypertonic saline, conducts electricity across the gap 361thereby indicating that the inner lip 312 may not be adequately sealed.The wires 360, 362 may be embedded in the body 302E or may travelthrough one or more of the lumens.

Referring to FIG. 57, another device 300F is shown which has two sets oflumens 364, 368 extending from both ends of the device 300F. The twosets of lumens 364, 368 perform the same functions as the lumensdescribed above and all discussion of the device 300 is equallyapplicable here. An advantage of using two sets of lumens 364, 368 isthat suction and/or fluid containment does not need to be maintained atall cells 304 at the same time. Connectors 370 at the buckle 308 aredisconnected to wrap the device 300F around the pulmonary veins and arethen reconnected to form the closed loop. Each set of lumens 364, 368terminates near the middle of the device 300F at ends 372. Valves 374are provided to selectively couple the lumens 362, 368 to the vacuumsource 318 and/or fluid supply 342.

Referring to FIGS. 49 and 52-57 the control system 334 is coupled to thetemperature sensors 336, ablating elements 311, fluid source 342 andvacuum source 318 for controlling the devices 300, 300E, 300F. Thecontrol system 334 may also be coupled to a pressure sensor 376 and/or aflow rate sensor 378 positioned along the inlet line of the vacuumsource 318 (FIGS. 56 and 57). The pressure and/or flow rate sensors 376,378 determine when the cells 304 are adequately secured to the tissue.If suction is not adequate, the pressure and/or flow rate will be higherthan expected. Fluid flow indicators 380 can also be used to measurefluid flow into and out of the devices 300E, 300F to determine whetherfluid is leaking from the cells 304 which also indicates a poor seal.

The cells 304 are preferably numbered and the control system 334indicates whether each cell 304 is adequately adhered to the tissue. Inthis manner, the user may apply manual pressure to a particular cell 304if an adequate seal is not present. The readout may be a digital readout377 or lights 379 for each cell 304. The control system 334 alsopreferably has a temperature display 335 and a timer 337 for timing theduration of ablation.

The control system 334 preferably activates the ablating elements 311 ina predetermined manner. In one mode of operation, ablation is carriedout at adjacent cells 304. Ablation may also be carried out at a numberof pairs of adjacent cells such as the first and second cells 304 andthe fifth and sixth cells 304. After ablation is carried out at theseadjacent cells 304, another pair or pairs of adjacent cells areactivated such as the third and fourth cells 304 and the seventh andeighth cells 304. The continuity of the ablation between the adjacentcells 304 may be confirmed in any suitable manner including thosedescribed herein. In another mode of operation, the control system 334energizes every other cell, every third cell or a limited number ofcells 304 such as no more than four. The control system 334 may alsoactivate less than 50% and even less than 30% of the total ablation areaat one time. For the device 300, a percentage of the total ablation areais essentially a percentage of the total number of ablation elements311.

The ablation at each cell 304 may be controlled based on temperaturemeasured at the temperature sensors 336. For example, the control system334 may be configured to maintain a near surface NS temperature of 0-80°C., more preferably 20-80° C. and most preferably 40-80° C. Thetemperature can be adjusted by changing the fluid flow rate andtemperature and/or the power delivered to the ablating element 311. Thecontrol system 334 may also have a multiplexer 333 which delivers energyto only the cells 304 having a temperature below the thresholdtemperature. Alternatively, the multiplexer 333 may deliver energy toonly the coldest cells 304 or only a number of cells 304 which registerthe coolest temperatures.

The control system 334 may also be configured to measure a temperatureresponse of the tissue to be ablated. The temperature response of thetissue is measured to provide a tissue characterization which can beused to select the appropriate ablation technique. The ablationtechnique is primarily selected to produce a temperature of at least 50°C. at the far surface FS of the tissue. When ablating cardiac tissue,for example, the control system 334 determines the ablation techniquerequired to form a transmural lesion which requires a far surface FStemperature of 50-80° C. and more preferably 50-60° C. Measuringtemperature at the far surface FS is somewhat difficult so thetemperature of the near surface NS is used in conjunction with themethods and devices described herein. Of course, the temperature of thefar surface FS may be measured to determine when the ablation iscomplete rather than using the temperature response described below.

The temperature response of the tissue is performed in the followingmanner. The tissue to be ablated is heated or cooled and the temperatureresponse over time is measured with the temperature sensors 336. Thetemperature response over time at the near surface NS provides a roughindication of the thermal properties of the tissue to be ablated. Thethermal properties of the tissue is affected by a number of variablesincluding tissue thickness, amount of fat and muscle, blood flow throughthe region and blood flow and temperature at the far surface FS. Thesefactors all play a role in the temperature response of the tissue. Thetissue thickness, for example, affects the temperature response in thefollowing manner. When a thin tissue layer is heated, the temperature atthe near surface will generally increase more slowly than with a thicklayer since the flow of blood at the far surface will draw heat awayquicker with the thin tissue layer. The control system preferablymeasures the temperature response for at least two temperature sensors336 for each ablating element with one of the temperature sensors beingpositioned laterally spaced to measure the temperature change atadjacent portions of the tissue.

After measuring the temperature change over time, the temperatureresponse is then analyzed to determine the appropriate ablationtechnique. The analysis may be a comparison of the temperature responsewith temperature response curves of known tissue types. The temperatureresponse curves may be developed empirically or may be calculated. Thetemperature response may also consider other variables input by the userincluding blood temperature and flow rate and the presence and amount offat. When assessing the temperature response during heating with theablating element, the amount of energy delivered to the tissue may alsobe used to characterize the tissue.

Using the results of the temperature response assessment, the controlsystem 334 determines the appropriate ablation technique to produce thedesired far surface FS temperature. In one mode of operation, thecontrol system 334 determines the amount of time required to reach adesired far surface FS temperature when the near surface NS ismaintained at a temperature of less than 60° C. The control system 334preferably maintains an adequate flowrate and temperature of fluid tomaintain the desired near surface NS temperature. The control system 334monitors the temperature of the near surface NS with temperature sensors336. After the period of time has elapsed, the control system 334automatically stops ablating. Alternatively, the ablation may take placeuntil the near surface NS reaches a target temperature. The continuityof the ablation may then be checked in any manner described herein.

In use, the devices 300, 300E, 300F are wrapped around a structure, suchas the pulmonary veins, with the locking mechanism 306 to form theclosed loop 307. The vacuum source 318 is then activated to adhere thecells 304 to the epicardium. Manual pressure can be applied to cells 304which are not sufficiently adhered to the tissue. The control system 334then ablates tissue while delivering fluid to cool the tissue andconduct RF energy to the tissue. The continuity of ablation is thenassessed by any suitable method including those described herein.

Referring to FIG. 58-63, still another device 400 is shown for ablatingtissue wherein the same or similar reference numbers refer to the sameor similar structure. The device 400 is particularly useful for ablatingcardiac tissue but may be used for any other purpose without departingfrom various aspects of the invention. In a specific embodiment, thedevice 400 is used to ablate tissue around the pulmonary veins. Theablating device 400 has a number of cells 402 similar to the cellsdescribed above and description of the preferred characteristics aboveare equally applicable here. For example, the cells 402 may have thepreferred dimensions and features of the cells 304 described above. Theablating device 400 has an ablating element 404 which is preferably anultrasonic transducer 406 although various features of the invention maybe practiced with any other type of ablating element 464 (FIG. 68).

The device 400 preferably delivers ultrasound which is focused in atleast one dimension. In particular, the device 400 preferably deliversfocused ultrasound having a focal length of about 2 to 20 mm, morepreferably about 2 to 12 mm and most preferably about 8 mm. Statedanother way, a focal axis FA is spaced apart from a bottom or contactsurface 405 of the device within the stated ranges. The focusedultrasound also forms an angle of 10 to 170 degrees, more preferably 30to 90 degrees and most preferably about 60 degrees as defined relativeto the focal axis A. The ultrasonic transducer 406 is preferably apiezoelectric element 408. The transducer 406 is mounted within ahousing 410. The housing 410 has an enclosure 412 and a top 414 whichfits over the enclosure 412. The enclosure 412 has curved lips 416 onboth sides of the enclosure 412 which generally conform to the curvatureof the transducer 406. The transducer 406 is curved to focus theultrasound energy for the reasons discussed below. The transducer 406has a length of about 0.43 inch, a width of about 0.35 inch and athickness of about 0.017 inch. The transducer 406 has a radius ofcurvature R (FIG. 62) consistent with the preferred focal lengthsdescribed above. The transducer 406 forms an angle A with the focus Fwithin the preferred angle ranges described above.

A layer 418, which is preferably aluminum but may be any other suitablematerial, is bonded or otherwise acoustically coupled to a concave side423 of the transducer 406. The layer 418 has a length of about 0.51inch, a width of about 0.43 inch and a thickness of about 0.012 inch.The layer 418 preferably has the same radius of curvature as thetransducer 406 so that the layer 418 mates with the transducer 406. Thelayer 418 is attached to the curved lips 416 of the enclosure 412 withan epoxy.

An advantage of using focused ultrasonic energy is that the energy canbe concentrated within the tissue. Another advantage of using focusedultrasound is that the energy diverges after reaching the focus therebyreducing the possibility of damaging tissue beyond the target tissue ascompared to collimated ultrasonic energy. When ablating epicardialtissue with collimated ultrasound, the collimated ultrasound energy notabsorbed by the target tissue travels through the heart chamber andremains concentrated on a relatively small area when it reaches theendocardial surface on the other side of the chamber. The presentinvention reduces the likelihood of damage to other structures since theultrasonic energy diverges beyond the focus and is spread over a largerarea.

Although the focused ultrasonic energy is preferably produced with thecurved transducer 406 and the layer 418, the focused ultrasonic energymay be produced with any suitable structure. For example, acousticlensing may be used to provide focused ultrasound. The acoustic lens canbe used with a flat piezoelectric element and matching layer.Furthermore, although the ultrasound energy is preferably emitteddirectly toward the tissue the ultrasound energy may also be reflectedoff a surface and directed toward the tissue without departing from thescope of the invention. The energy may also be produced by a number ofsmall transducers which are oriented to focus or concentrate ultrasonicenergy, such as at least 90% of the energy, within the preferred angleranges and radius of curvature described herein when viewed along alongitudinal axis 419 or along the focal axis FA. For example, amultielement acoustic phased array may be used to provide an acousticbeam-steering capability from one or more cells. One skilled in the artcan also appreciate the use of multiple matching layers, focusingacoustic lenses and non-focusing acoustic windows and the like. Thus,the focused energy may be produced in a number of different ways,including other ways not mentioned here, without departing from thescope of the invention.

A distributing element 420 is attached to the transducer 406 at twolocations to distribute energy that drives the transducer 406. Theelement 420 is preferably a piece of copper ribbon 0.020 inch wide and0.0005 inch thick soldered to the transducer 406 at two locations. Acoaxial cable 422 delivers power to the transducer 406 from a source ofpower 421 and also provides a ground path. The coaxial cable 422 has apower lead 424 coupled to the distributing element 420 to power thetransducer 406. A braided portion 426 of the cable 422 serves as aground. The braided portion 426 is soldered to a tube 428 and/or the top414. The ground path leads from the transducer 406 to the layer 418 andthen to the housing 410 at the curved lips 416. The ground path thenpasses to the top 414 and finally to the braided portion 426 eitherdirectly or via the tube 428. The tube 428 and top 414 are preferablymade of brass and the enclosure 412 is preferably made of aluminumalthough any other suitable materials may be used. Polyimide tape 430 isadhered to the inside of the enclosure 412 and on the transducer 406 toelectrically separate the two structures.

The transducer 406 may be cooled during operation although cooling maynot be required. A cooling inlet 432 having an inlet lumen 440 extendsthrough the top 414 and is coupled to a source of cooling medium 434.The cooling medium, which is preferably forced air, passes into achamber 436 so that the cooling medium is in direct contact with thetransducer 406. A cooling outlet 438 having an outlet lumen 442 removesthe cooling medium from the chamber 436. Although the lumens 440, 442are preferably separate and independent from the housing 420, the lumens440, 442 may also be integrated into the housing 420 without departingfrom the scope of the invention.

The cells 402 may also be adhered or acoustically coupled to the tissuewith suction in the manner described above although various features ofthe invention may be practiced without using suction. The housing 410 ismounted within an opening 446 in a suction body 448. The body 448 has aport 449 coupled to a lumen 452 leading to the vacuum source 318. Thelumen 452 is coupled to the outlet lumen 442 with tubing 443 so that theoutlet lumen 442 provides suction and withdraws the cooling medium (FIG.59). Of course, the lumen 452 may also be completely independent of theoutlet lumen 442. FIG. 58 shows separate cooling outlet and vacuumlumens. The port 450 leads to recesses 454 on two sides of thetransducer 406. The recesses 454 also may be formed by individualsuction pods, a linear segment, or any other suitable structure withoutdeparting from the scope of the invention. A channel 456 extends fromone side of the enclosure 412 to provide communication between the tworecesses 454. The channel 456 prevents only one recess 454 from beingadhered to the tissue. The body 448 is preferably made of polycarbonatebut may be made of any other suitable material.

The ablating device 400 may also be used with a substance, such as a gelor saline, applied to the target tissue to eliminate air gaps betweenthe transducer 406 and target tissue. Air gaps between the transducer406 and target tissue impede delivery of ultrasonic energy to thetissue. When using suction as described below, use of the substance maybe unnecessary since the transducer 406 assembly can be forced intointimate contact with the target tissue with the suction force.

The ablating device 400 may also have a membrane 460 (FIG. 64) filledwith the substance 458 or a solid element 459 (FIG. 65) which transmitsthe ultrasonic energy to the tissue. An advantage of the membrane 460 isthat the membrane 460 may be made flexible and compliant to conform tothe tissue. Another advantage of the membrane 460 is that the distancebetween the transducer 406 and the tissue may be varied. When ablatingthick tissue, the membrane 460 can be deflated so that the transducer406 is close to the tissue (FIG. 64). When ablating thin tissue, themembrane 460 is inflated so that the transducer 406 is further from thetissue (FIG. 66). Adjacent cells preferably maintain contact with thetissue to maintain the orientation of the device. The membrane 460 mayalso be inflated and deflated during or between activations of thetransducer 406 to move the focus relative to the tissue. For example,the membrane 460 may be inflated and deflated to move the focus relativeto the tissue and, in particular, to different depths. The membrane 460is adhered to the device around the bottom of the enclosure 412. Themembrane 460 is preferably compliant and may be made of any suitablematerial such as silicone or urethane. The membrane 460 may bepre-filled with the substance or the substance may be added laterthrough another lumen (not shown).

Referring to FIG. 67, the membrane 460 may also take a shape which tiltsthe transducer 406. The transducer 406 is preferably tilted to directthe ultrasound energy to tissue positioned beneath gaps between adjacenttransducers 406 as will be explained in greater detail below. A flexibleflange 461 deflects to permit tilting of the device. The transducer 406may be angled, pivoted or tilted in any other suitable manner. Forexample, the transducer 406 may have a mechanical pivot which moves thetransducer 406 or a movable foot on the bottom of the device 400 whichis advanced and retracted to tilt the transducer 406.

Referring to FIG. 68, another device 462 for ablating tissue is shownwherein the same or similar reference numbers refers to the same orsimilar structure. The device 462 has the ablating element 404 which ispreferably an ultrasonic transducer 463. The transducer 463 is designedto deliver ultrasonic energy to tissue beneath the transducer 463 and totissue beneath the gaps between adjacent cells 402. In this manner, thedevice may be operated without moving or tilting the transducers 463 tocreate a continuous lesion beneath the device. The transducer 463 is aflat transducer 463 with a layer 464 attached thereto. The layer has aflat bottom portion 466 and angled sides 468 which direct energy attissue lying beneath the gaps between adjacent transducers 463. Thedevice 462 has a membrane 470 adhered over the bottom of the cell 402.The membrane 460 is filled with a substance 472, such as a gel orsaline, which transmits the ultrasonic energy to the tissue. The device462 may be operated in any mode or method described herein.

Referring to FIGS. 69-70, another transducer 474 is shown which may beused with any of the devices described herein and is particularly usefulwith the devices of FIGS. 59-68 and all uses and features of the devicesdescribed herein are incorporated here. The transducer 474 preferablyprovides focused ultrasound relative to a focal axis FA within focallengths and/or angle ranges described above. The transducer 474 alsoprovides diverging ultrasound energy when viewed along an axistransverse to the focal axis (FIG. 70). The ultrasound diverges to forman angle A2 of about 10 to 120 degrees and preferably about 45 degrees.The focused and diverging ultrasound is preferably formed with thesaddle-shaped transducer 474 with a similarly shaped layer 476 attachedor otherwise acoustically coupled thereto. Of course, the focused anddiverging ultrasound may be produced in any other suitable mannerincluding those described herein. An advantage of the diverging natureof the ultrasound energy is that tissue lying beneath gaps between cellscan be ablated with the ablating elements while still providing arelatively focused energy. The term focal axis FA, as defined herein, isintended to include both linear and non-linear shapes. For example, thefocal axis FA of the transducer of FIGS. 69 and 70 is curved.

Referring to FIGS. 71-73, still another ablating device 478 is shownwherein the same or similar reference numbers refer to the same orsimilar structure. The ablating device 478 has a first ablating element480, a second ablating element 482 and a third ablating element 484which differ. Although only three different ablating elements are shown,the device 478 could include any number of ablating elements. Theablating elements differ to provide different ablating characteristics.For example, the ablating elements may produce focused ultrasound withthe first ablating element having a different focal length than thesecond or third ablating elements. Such a configuration permits the userto select the appropriate ablating element for the particular tissuestructure. The ablating elements 480, 482 and 434 may also be designedto operate at different frequencies and/or powers.

The ablating elements are movable within a lumen 486 in a body 488. Thebody 488 forms two suction channels 490 to adhere the device to thetarget tissue. The body 488 preferably forms a closed loop but may beshaped in any other manner. Each of the ablating elements has an element492 which transmits the ultrasound energy to the target tissue. Theablating elements may also have the membrane (see FIG. 64) or may beused without the element or membrane (see FIG. 60). Lumens 491 forsupply of energy, suction and inlet and outlet for the cooling mediumare provided. The lumens 491 extend through a manipulator 493. Themanipulator 493 forms a seal with the body 488 to adhere the body 488 tothe tissue with a suction.

An advantage of using ultrasound for ablation is that the transducer mayalso be used to measure temperature. Measuring temperature isparticularly helpful in operating the transducer for feedback control ofthe ablating element in any manner described above. Of course, thethermocouples described above or any other suitable methods or devicesfor measuring temperature may be used.

Another advantage of using the transducer is that the transducer can beused to determine whether the transducer itself is in good contact withthe tissue to be ablated. Any air gap between the transducer and thenear surface NS can dramatically affect the ability to deliver theultrasonic energy in a controlled manner. The adequacy of contact isdetermined by measuring the electrical impedance which is generallylarge when an air gap exists between the transducer and tissue.Monitoring suction as described above is another method of assessingcontact between the device and tissue.

Yet another advantage of using the transducer is that the transducer canprovide flow velocity data using conventional doppler techniques. Thedoppler flow techniques can be used to characterize the amount ofcooling at the far surface FS which can be used to select theappropriate tissue ablation technique.

Still another advantage of the transducer is that the transducer canprovide the thickness of one or more layers of tissue using knownpulse-echo or a-line techniques. For example, the transducer may beoperated to provide total tissue thickness or the thickness of fat andmuscle or other layers. The thickness of fat, muscle, and totalthickness may be used when characterizing the tissue to determine theappropriate ablation technique. For example, the ablating element may beoperated in response to the tissue thickness measurement with or withoutone or more additional measurements. A single transducer may be used toemit ultrasonic energy and receive reflected energy or one transducermay emit and a different transducer can receive the reflected ultrasoundenergy.

The transducer may also be used to determine the distance to tissuebeyond the target tissue such as endocardial tissue on the opposite sideof a cardiac chamber. Such measurements can be useful in selecting theappropriate transducer. For example, if the tissue structure beyond thetarget tissue is relatively far away, a longer focal length can be usedsince the ultrasound energy will be spread over a larger area. On theother hand, if the tissue structure is near the target tissue, shorterfocal lengths may be preferred to avoid damaging the tissue structurebeyond the target tissue.

These above-described aspects of the ablating element may be combinedwith any of the other features and advantages of the invention. Forexample, the transducer 406 may be used for temperature feedback controlof the control system 334 in any manner described herein and the flowvelocity measurements may be used to characterize the amount of bloodcooling at the far surface FS.

A method of ablating tissue is now described. The method is described inconnection with the ablating device 400 described above, however, themethod may be practiced with any other suitable structure or device. Theablating device 400 is positioned against tissue to be ablated andsuction is initiated to hold the cells 402 to the tissue to be ablated.The ablating device 400 may use any of the methods and devices describedabove, such as temperature feedback control or methods of checking theadequacy of contact, which are incorporated here. As will be explainedbelow, the transducer 406 itself may be used to determine the adequacyof the contact between the device and the tissue. In particular, thetransducer 406 may also be used to determine whether any air gaps existbetween the transducer 406 and the tissue. After it has been determinedthat the cells 402 are adequately adhered to the tissue, one or more ofthe cells 402 are activated to begin ablating tissue.

In another aspect of the invention, the device is operated during twodifferent time periods while varying at least one characteristic of thedevice such as the frequency, power, position of the focus relative tothe tissue and/or ablating time. For example, the ablating device 400may be operated at varying frequencies over time to ablate tissue in acontrolled manner. Specifically, the ablating device is preferablyoperated to create a transmural lesion by controlling the delivery ofenergy to the tissue. Although it is preferred to vary the frequencywhen ablating the tissue, the device may, of course, be operated at asingle frequency without departing from various other aspects of theinvention

In a first treatment method of the present invention, the transducer 406is activated at a frequency of 2-7 MHz, preferably about 3.5 MHz, and apower of 80-140 watts, preferably about 110 watts, in short bursts. Forexample, the transducer 406 may be activated for 0.01-1.0 second andpreferably about 0.4 second. The transducer 406 is inactive for about2-90 seconds, more preferably 5-80 seconds, and most preferably about 45seconds between activations. In this manner, a controlled amount ofaccumulated energy can be delivered to the tissue in short bursts toheat tissue at and near the focus and minimizes the impact of bloodcooling at the far surface FS. Ablation at this frequency may continueuntil a controlled amount of energy is delivered such as about 0.5-3kilojoules. Treatment at this frequency in relatively short burstsproduces localized heating at the focus. At the first frequency, energyis not absorbed as quickly in tissue as it is at higher frequencies sothat heating at the focus is not significantly affected by absorption ofultrasound energy in tissue before reaching the focus.

Following treatment at the first frequency, the transducer 406 isoperated for longer periods of time, preferably about 1-4 seconds andmore preferably about 2 seconds, to ablate tissue between the focus andthe transducer 406. The frequency during this treatment is also 2-14MHz, more preferably 3-7 MHz and preferably about 6 MHz. The transducer406 is operated for 0.7-4 seconds at a power of 20-60 watts, preferablyabout 40 watts. The transducer 406 is inactive for at least 3 seconds,more preferably at least 5 seconds and most preferably about 10 secondsbetween each activation. In this manner, a controlled amount of energycan be delivered to heat tissue between the focus and the transducer.The treatment at this frequency may continue until a controlled amountof total energy is delivered such as about 750 joules.

As a final treatment, the ultrasonic transducer is activated at a higherfrequency to heat and ablate the near surface NS. The transducer ispreferably operated at a frequency of at least 6 MHz and more preferablyat least 10 MHz and most preferably about 16 MHz. The transducer 406 isoperated at lower power than the treatment methods above since theultrasonic energy is rapidly absorbed by the tissue at these frequenciesso that the near surface NS is heated quickly. In a preferred method,the transducer is operated at 2-10 watts and more preferably about 5watts. The transducer 406 is preferably operated until the near surfaceNS temperature reaches 70-85 degrees C.

Each of the treatments described above may be used by itself or incombination with other treatments. Furthermore, the combination oftransducer size, power, frequency, activation time, and focal length mayall be varied to produce the desired delivery of ultrasound energy tothe tissue. As such, it is understood that the preferred embodiment maybe adjusted by simply adjusting one or more of the characteristics and,thus, these parameters may be changed without departing from variousaspects of the invention. The treatment sequence described abovegenerally deliver energy closer to the near surface NS during the secondtreatment and even closer to the near surface NS for the thirdtreatment.

The focus of the ultrasound energy may also be moved relative to thetissue to deliver energy to different depths in the tissue. When usingthe devices of FIGS. 66 and 67, for example, the device can be movedcloser to and farther away from the target tissue with the membrane 460conforming to the required shape to fill the gap between the transducer406 and the tissue. The membrane is preferably inflated and deflated tomove the focus, however, the device may also be moved with any othersuitable mechanism such as the threaded foot described above. The focusmay be moved while the ablating element is activated or may be movedbetween activations of the ablating element. Moving the focus of theultrasound energy may be sufficient to create a transmural lesionwithout changing frequencies or may be used together with a change infrequencies as described above. The focus may be moved in any othermanner such as with a phased array or variable acoustic lensing.

Referring again to FIG. 60, after the ablating elements have beenactivated to ablate tissue it may be necessary to ablate tissue in gapsbetween ablations from each of the cells. In one method, the entiredevice is shifted so that each of the ablating elements is positioned toablate tissue beneath one of the gaps. Thus, after ablating tissue withall of the cells, the device is shifted and all of the cells areactivated again to create a continuous lesion. Another method to ablatetissue beneath the gaps is to tilt the cells to ablate tissue beneaththe gaps. In this manner, the device does not need to be moved. Whenusing the device of FIG. 67, for example, the membrane is inflated totilt the transducer which directs the ultrasound energy toward tissuebeneath gaps between transducers.

The control system 334 may be designed to automatically ablate in anymanner described herein. For example, the control system can change thefrequency, power, focal length and/or operating time to provide thedesired ablating technique. The change in frequency and power may becompletely automatic or may require some user input such as visualindications of fat and/or tissue thickness. For example, the controlsystem 334 may be designed to automatically sequence through two or moredifferent ablating techniques such as those described above. Othertechniques, of course, may be used depending on the tissuecharacteristics and the type and characteristics of the one or moreultrasound transducers 406. The control system 334 may also utilizefeedback, such as temperature-based feedback or electrical impedance, toactively control the ablations. Furthermore, although various methodshave been described, the corresponding functionality of the controlsystem is provided. Thus, all methods of the present invention providecorresponding devices and systems as controlled by the control system.

In still another aspect of the present invention, a cover 500 isprovided in which an ablating device 502 is positioned during initialpositioning of the device as shown in FIG. 74. The cover 500 may extendover only the bottom or contact surface of the ablating device 502 ormay be a sleeve 501 which surrounds the device 502. The ablating device502 may be any of the ablating devices, elements or systems describedherein or any other suitable system and all aspects of the ablatingdevices described herein are incorporated here specifically for theablating device 502. The cover 500 has a cavity 503 which contains aflowable material 504. The flowable material 504 provides an interfacebetween the ablating device 502 and the tissue to be ablated. Theablating device 502 is loaded into the cover 500 to help reduce oreliminate air bubbles or gaps contained in the flowable material 504.Air bubbles or air gaps can reduce the performance of various energysources such as RF and ultrasound.

The cover 500 is positioned at or near the desired ablating location andthe cover 500 is then pulled, retracted or otherwise moved to expose theablating device 502. When the cover 500 is moved to expose the ablatingdevice 502, the flowable material 504 conforms to the shape of thetarget tissue to provide an interface of the flowable material 504between the ablating device 502 and the target tissue. The cover 500 ismoved by simply pulling the sleeve over the end of the ablating device502 while maintaining the ablating device in substantially the desiredablating position. Alternatively, the ablating device 502 may be movedout of the cover 500, however, removal of the cover 500 is preferred toprevent loss of the flowable material 504 as the ablating device 502 ismoved along the target tissue. The flowable material 504 may be anysuitable material depending upon the ablating energy being used. Whenultrasound energy is used, the flowable material is preferably PEG(polyethyleneglycol) or glycerine. The flowable material also preferablyhas a relatively high boiling point such as at least 100 degrees C. anda vapor pressure lower than that of water.

In still another aspect of the present invention, the ablating device502 may also have a tip 510 which provides a flexible, atraumatic distalend as shown in FIG. 74. The flexible tip 510 facilitates advancement ofthe device 502 through the space between the epicardium and pericardiumwithout damaging the heart or pericardium. The tip 510 may be removableso that the tip 510 does not interfere with the ablating process and canmake it easier to form a closed loop as is shown in various embodimentscontained herein. It can be appreciated that the tip 510 may be usedwith any of the ablating devices, systems or methods described hereinwithout departing from this aspect of the invention. The tip 510preferably has a length of at least two inches and more preferably atleast four inches from the distal end 511. The tip 510 is preferablyfree of any ablating elements.

In another aspect of the present invention, another system and methodfor ablating tissue is shown in FIGS. 75 and 76. The system 512 providesa liquid environment around the heart. The liquid environment may helpin energy transfer when using certain energy types, such as RF orultrasound, and/or may serve to simply eliminate air bubbles or gapswhich can hinder energy transfer. The liquid environment also helps incontrolling the temperature since the temperature of the liquid can beregulated. For example, the liquid can be circulated through a heatexchanger 514 which heats or cools the liquid as desired. In one aspectof the invention, the liquid is cooled to remove heat generated by theablating device 502. The temperature may be controlled in any mannerdescribed herein and such methods are specifically incorporated here.

The system 512 includes a liquid delivery element 516, such as a tube518, connected to a liquid source 520, preferably sterile saline. Ofcourse, the liquid must also be delivered and/or withdrawn with theablating device 502. Liquid is delivered as necessary with conventionalvalves 522 and clamps 524 controlling the flow of liquid. The ablatingdevice 502 is submerged within the liquid environment and may be anydevice described herein or other suitable device. The liquid deliveryelement 516 may form a fluid tight seal with the pericardium or thepatient may be positioned so that the liquid environment can be createdby penetrating the pericardium at an elevated position which does notrequire a hemostatic seal. The system 512 may be used in an open chestprocedure with a rib retractor 515 as shown in FIG. 76. The pericardiumis snared, sutured or otherwise anchored or suspended as is known in theart. The system 512 may also be used in a less or minimally invasivemanner as shown in FIG. 75 wherein the chest is accessed via asubxyphoid approach. The delivery element 516 has two lumens with one ofthe lumens 517 being an outlet lumen coupled to openings 519.

In another aspect of the invention, any of the ablating devicesdescribed herein may have a convex contact surface 520 as shown in FIGS.73 and 74. The convex contact surface 520 helps to squeeze or eliminateair bubbles or gaps from the area between the device and the targettissue. Air bubbles or gaps can inhibit energy transfer and, inparticular, can reduce the efficiency of ultrasound and RF energytransfer. The convex surface 520 may form part of the ablating elementitself or may be a separate element that is adhered, mounted orotherwise coupled to the ablating device as described above. Of course,the convex contact surface 520 may be used with any of the ablatingdevices described herein and is shown specifically in FIGS. 73 and 74.The convex contact surface 520 may be made of any suitable material suchas polyurethane.

Referring to FIGS. 77 and 78, another ablating device 522 is shown whichis similar to the device of FIG. 64 wherein all aspects of the device ofFIG. 64 are incorporated here. The ablating device 522 has the membrane460 which is spaced apart from the ablating element to form a fluidcavity 524 therebetween. The fluid cavity 524 contains a fluid 526 whichcan serve any one or more of the following functions. The fluid 526, ofcourse, transmits energy from the ablating element. The membrane 460also conforms to the shape of the target tissue. The fluid 526 may bedelivered from the source of cooling medium 434 having a suitable heatexchanger as discussed above. The temperature of the fluid 526 may becontrolled in any manner described herein and all such descriptions areincorporated specifically here for all purposes. For example,temperature control of the fluid provides the ability to control thenear surface temperature of the tissue in any manner described herein.

Referring to FIG. 77, each fluid cavity 524 may extend over a singleablating element with each of the fluid cavities 524 being coupled to acommon inlet lumen 530 and outlet lumen 531. Alternatively, the membrane460 may extend over a number of ablating elements or along the entiredevice as shown in FIG. 78. The fluid 526 is circulated through thefluid cavity 524 from an inlet lumen 525 attached to one end and anoutlet lumen 527 attached to the other end of the device. The fluid 526is circulated through the fluid cavity 524 using the source of coolingmedium 434. The membrane 460 may also have openings 462 (FIG. 77)therein or may be permeable so that some of the fluid 526 leaks throughthe membrane 460. The fluid 526 may help conduct energy or may simplyreduce or eliminate air gaps. The membrane 460 may also form the convexcontact surface 520 naturally or when fluid pressure is applied. Thefluid 526 may also be pulsed to provide intermittent weeping or leakingof the fluid through the membrane 460. The pulsed fluid flow may also beused to deform the membrane by partially inflating/deflating themembrane which may help to sweep away bubbles or provide a flushingaction for the fluid.

Referring now to FIG. 79, a flexible skirt 536 may be provided aroundthe ablating element. The flexible skirt 536 may be used to contain thefluid 526 which is supplied in any suitable manner such as thosedescribed herein. Referring to FIG. 80, the flexible skirt may be usedin connection with the convex contact surface 520. The fluid 526, orother flowable material, is introduced through an inlet 540 and travelsdown lumen 542 to the contact surface 520. The skirt 536 helps tocontain the fluid 526 to inhibit the fluid 526 from flowing freelyoutward.

Finally, although the present methods have been described in connectionwith creating a continuous lesion around the pulmonary veins, it isunderstood that the methods are equally applicable for only ablatingpartially around the pulmonary veins or along only a segment.Furthermore, other lesions may be beneficial in treatingelectrophysiological conditions and the devices and methods describedherein may be useful in creating such other lesions. Thus, the presentinvention should not be construed as being limited to creating lesionscompletely around the pulmonary veins.

While the above is a complete description of the preferred embodimentsof the invention, various alternatives, substitutions and modificationsmay be made without departing from the scope thereof, which is definedby the following claims. For example, any of the ablating devicesdescribed herein may have the anchor, fins, lateral balloons, sensors,and/or electrodes without departing from the scope of the invention.

1-41. (canceled)
 42. A method of ablating tissue, comprising the stepsof: providing an ablating device having a convex contact surface;positioning the convex contact surface adjacent to an epicardialsurface; ablating the epicardial tissue after the positioning step. 43.The method of claim 42, wherein: the providing step is carried out withthe ablating device comprising an ultrasonic transducer.
 44. The methodof claim 43, wherein: the providing step is carried out with the convexsurface being formed by an element mounted to the ultrasonic transducer.45. The method of claim 44, wherein: the providing step is carried outwith a membrane forming the convex surface.
 46. The method of claim 45,wherein: the providing step is carried out with the membrane partiallydefining a cavity containing a fluid.
 47. The method of claim 42,wherein: the providing step is carried out with the ablating devicehaving a plurality of ablating elements.
 48. The method of claim 42,wherein: the providing and moving steps are carried out with theablating device forming a closed loop around the heart.
 49. The methodof claim 48, wherein: the providing and moving steps are carried outwith the ablating device forming a closed loop around the pulmonaryveins; and the ablating step is carried out to form an ablation aroundthe pulmonary veins.
 50. An ablating device for ablating tissue,comprising: a body; an ablating element coupled to the body; a membraneextending over at least part of the ablating element, the membrane beingspaced apart from the ablating element to form a fluid cavity; and thefluid cavity containing a fluid.
 51. The ablating device of claim 50,further comprising: a fluid source coupled to the fluid inlet forcirculating the fluid through the fluid cavity.
 52. The ablating deviceof claim 51, further comprising: a heat exchanger having an inlet whichreceives the fluid and an outlet which returns the fluid to the fluidcavity.
 53. The ablating device of claim 50, wherein: the membrane formsa convex contact surface.
 54. The ablating device of claim 50, wherein:the membrane forms the convex contact surface with fluid pressure. 55.The ablating device of claim 50, wherein: the membrane permits some ofthe fluid to pass therethrough to wet the target tissue with the fluid.56. The ablating device of claim 50, wherein: the membrane extends overmore than one ablating element.
 57. An ablating device for ablatingtissue, comprising: a body; an ablating element coupled to the body; aflexible skirt surrounding at least a portion of the ablating element;the fluid cavity containing a fluid.
 58. The ablating device of claim57, further comprising: a fluid delivery channel which delivers fluid tothe fluid cavity.
 59. The ablating device of claim 57, wherein: the bodyhas a contact surface on a bottom side, the contact surface beingconvex.
 60. (canceled)